I know this might be dumb and many people have this idea. But I think Kat actually left him. I know Kat is slow but she could easily get any shitty job, and has proven to get new jobs after she loses one. Also Jasper hasn't been seen for months now. I know Dave wants to say its because Kat is home so Jasper stays with her but I don't buy it. Plus Jasper has been in Phil's room when Kat was home so I find it weird that she is home now and Jasper never goes to Phil. Although he says the door is closed, but I think that is a cover up. So I think she left him recently and took Jasper.
Now he is walking? Wouldn't that be time he would be spending time with his wife? He has said how important it is to be with her and that he has no time to improve his streams or anything else because he needs that bonding time with Kat. Now he has time to go for walks. Maybe he walks now for various reasons, maybe he thinks if he "exercises" that Kat will see he is a new better human being and take him back or the depression of Kat leaving him is too much so he walks to distract from that.
This is just a hunch and there is not much evidence of this but, we saw something similar happen when he and Pandalee broke up and when she left. I can't recall when was the last time we heard Kat talk with Phil during those live mic moments, but I believe it was a few months ago. So I speculate she left when Jasper started disappearing which was about 2 months ago I think. It could explain why he gets super annoyed recently when someone mentions Kat and her job status because it reminds him his horse galloped away from the barn.
Either way I am going to keep an eye of any odd behavior from Phil and anything he says about Kat. This wouldn't be the first time Phil lied to his audience that his significant other left him but played it as she was still home. But who knows.
Edit: Also when Phil goes on break or steps out of the room we never see Jasper come in and jump on his chair/boxes which he has done plenty of times before. Unless Kat has Jasper in a vice grip and never letting go.