Khet isn't exactly like Phil, but the two are similar, and I think their complete lack of romantic desires is a shared trait. We can't apply normal relationship logic to either of them. Leanna was ultimately unhappy because she had more traditional desires, like actually leaving the house. Khet, much like Phil, seems pretty happy playing house. She can lie and delude herself into thinking she's a productive and mature adult because she has a home, a husband and a job. Those are all things successful and mature adults are supposed to have. She just ignores the fact the home is a middle unit condo that's filthy and filled with broken appliances, her husband is someone she maybe spends a few hours with each week and sleeps in a separate bed from her and her job is a basic store clerk who only works around 20 hours a week.
Basically, Leanna was unhappy because she had standards and wanted something from her life. That's why the older she got, the more the mask lifted and she realized what life with Phil was like/how unusual her relationship was compared to other people. She was also actively trying for the last year or so to make things work with Phil, and Phil was pretty vocal about it because Phil always overshares. It doesn't sound like Khet has ever nagged him to have a date night or anything. And it sounds like the few conversations they have is basically shared venting about whatever minor grievances annoy them, followed by watching other YouTubers and playing mobile games. I think they talk at, not with, each other, and probably don't really listen to what the other person is saying.
Khet has a history of cheating since that's basically how she met Phil, but think about how that actually played out. She wasn't cheating because she wanted sex, otherwise, she'd have picked someone who was actually local, not all the way up in Seattle. I don't think it was entirely her being a gold digger either. While she wants Phil for the fact he can provide her with food and a place to live, I think she also wanted an enabler who would fully support her hermit lifestyle while also pretending she's a mature adult without her having to actually do anything.