I want to give some advice outside of what everyone else has been saying (she's probably a whore, you're better off without her, she wasn't meant for you anyway, etc.)
Relationship dynamics are often not well understood by alot of people, myself included. I didn't have a good example of a healthy relationship growing up and I had to navigate my own relationships based on this limited understanding of how they work. As I've gotten older I like to think I have a better understanding of how it works.
Every relationship has a power dynamic, meaning there is usually someone who has more power than the other. This translates to: whoever is more emotionally invested in the relationship has the lower power position.
Most healthy relationships have the man slightly up in the power position, meaning he is the one who is deciding how the relationship will progress, and the woman is the one trying to get the man to signal commitment. This is why women will brush off men who signal commitment early (nice guy behavior) in favor of men who are more withdrawn/mysterious. You can't do this forever, obviously, because women will think that you don't care about them after a while, or that you are just playing them.
A man showing his commitment is a form of willfully forfeiting some of his power in the relationship dynamic to signal his attachment to the woman. This is why we get down on one knee to propose. This is why we write songs and do other gay shit for women. We are essentially trading our sense of emotional independence and freedom for a woman's security in the relationship.
The issue is that when someone feels too secure in a relationship, attraction can suffer as a result. Women will begin to pull away when a guy is too available, too vulnerable, etc. The guy will often try to close this distance and in the process, drive her even further away. She might point out things he is doing wrong, and he might correct these things, only for her to just find other reasons to push him away.
In the beginning of a relationship, there is an intense feeling called limerance. This is what drives people to fall in love with eachother during the first several months of a new relationship. Limerance is essentially 70% Hope + 30% Uncertainty. We are excited by the chance of being with a new person, but we simultaneously feel a sense of uncertainty about how it will play out.
The anticipation of being with someone new is tempered by the fear of it not working out, and it creates a cocktail of emotions that make the other person addictive in a sense. Without the uncertainty, the excitement naturally wanes as the relationship becomes more familiar and secure.
While this feeling naturally dissipates over time as a new relationship crystallizes into a partnership, it often returns after a breakup.
You are experiencing a form of limerance over the loss of your girlfriend. It's probably 70% Uncertainty + 30% Hope. She is probably all you can think about, and you probably feel like shit and have a hard time sleeping and eating. Part of you thinks it's over, and maybe a small part of you thinks she will come back.
Everyone in this thread has pointed to her recent behavior as evidence that she was never the one for you, and maybe she wasn't, but I bet when the relationship was good, and the dynamic was right, she was probably very lovely and good to you. You remember this version of her and have a hard time reconciling it with the version you're getting now. Your actions are being motivated by a fear of loss and logic, but the reality is that there isn't any text you can send that will make her change her mind at this time. Only your behavior after this will be a factor in whether or not you see her again.
The truth is, after a breakup, she has all the power in this dynamic. She feels strong because she's the one who walked away. She probably feels like she can get you back at any moment. She's probably right. She's feeling alot of relief right now, and that is being egged on by her girlfriends. Single women are known to pressure and encourage their friends to be single as well because it makes them feel better about themselves.
When we experience a sense of loss, we tend to reevaluate our relationships. Maybe you had a troubled relationship with a family member, but when they passed away, you still mourned them, and remembered the good times. This works with breakups as well. You probably remember all the good things about her more than the bad. This can work for you as well as for her.
The best thing you can do right now is focus on yourself. You won't be able to flip a switch and not give a shit about this girl anymore, and you are experiencing alot of grief, but if you can project strength, even if you don't feel it, that's the best effort you can make to either move on or get her back. Not begging, pleading, or any kind of grand gesture.
She might be seeing other dudes right now, or is even in another relationship. This could be a rebound, and if it is, it probably won't last. If she left you for another guy, it will more than likely not work out. If that's the case, I wouldn't take her back. If you try to convince her to come back or talk about the relationship while she is seeing someone else, you are making the other guy look good by comparison. You may have already done this, and that's okay, but you need to stop this immediately if so.
Don't text her, don't make efforts to communicate with her, and if you see her irl, just pretend she's an acquaintance and keep things short and sweet. If the relationship was meaningful, once she experiences that sense of loss of you (this will probably take months) she will probably start to wonder about you. She will probably reach out. She won't tell you that she misses you and wants you back, she'll probably just ask you how you are doing or wish you a happy birthday. She might ask if you want to be friends. Hell, she might even tell you about her new guy. At this point, she isn't sure if she wants you back, she just wants to see that she still has access to you. She is trying to determine her standing in the power dynamic.
When she does reach out, again, just treat her like a friend. Take a while to respond, be funny and relaxed, but don't try to use emotional language or bring up the relationship. When she notices that she doesn't have power over you like she once did, and she has lost access to you, she will probably start finding more random excuses to reach out to you. You will shift from the guy she dumped to the guy she let slip through her fingers.
More than likely, if you start seeing someone else, it will trigger that sense of loss in her that much more ("I thought you loved me, I thought you would wait for me") I've seen this happen irl dozens of times. Girl dumps guy, guy finds another girl, girl wants him back. The same shit happens with men breaking up with women too.
By pulling away and focusing on yourself, it's the best strategy to both move on from her and also get her back if that's what you want. You are putting yourself in the mindset that you don't need her and that makes you not only more attractive to her, but to other women and also yourself.
If for some reason she crashes out and tells you how much she loves and misses you, you might be inclined to just drive over to her place and kiss her in the rain or some other romantic shit. Don't.
Make her earn you back. Tell her you are open to see her again, and do something casual like coffee or a walk in the park. Remember the guy she fell for and be that guy again. Not just for her, but yourself. Take things slow and don't bring up the relationship unless she does. She will probably bring up the good memories and not the bad ones. This is a sign that she truly wants you again.
The most important thing to remember is that the real person you need to get back isn't your girlfriend, it's yourself. This will take time and effort, both of which will feel like they are in short supply to you. This isn't true. You might feel like there is only a small window to get her back, but that's not the case. You might not feel like going out and doing things, but as you do, you will feel better.
Best of luck brother. We have all been there before.