Nah, he's right about that. That question is a shit test. If you say another woman, you'll forever owe her, but Drex's answer reflects that shit test right back on her. Her response at that point should be that it was a hypothetical question... if she actually agrees and goes through with it, she's no longer "your girl." You should be peacing out of that "relationship."
If you wanna invite another dude to come over and eiffel tower the ho, though, that's up to you. You can call that gay if you want, I'm not judging one way or the other. Main point should be that you end the relationship either way. She can be a ho with or without you, just don't marry yourself into it. And don't catch anything that a round of antibiotics won't take care of.