I’m a police officer on response, and on certain weeks where I work a full set of late shifts I don’t see my husband and kids for 5 days )in normal times when they are at work/school).
Sometimes I’m 5+ hours late off. I miss birthdays, social events, class assemblies, romantic meals, date nights, parents evening. It’s a bit of a cliche but it really is more than a job. I love what I do and would never consider giving it up. Most of my colleagues are the same. To make a marriage or relationship work, the non-police partner sort of has to accept that they won’t come first, or that plans will be cancelled or that their partner won’t be there for an occasion where you’d like them to be. It’s not for everyone, and if you want more then that’s absolutely your right. But I don’t think your partner will change.
It’s not ok for him to be going back on promises made, but I think ultimately it will come down to your decision to either accept things as they are, or not. It is really tough being the partner of a police officer and I know how lucky I am to have the support of my DH (who is very proud of what I do). Only you can decide.
Just on two other points, pay in the police is based on rank and time served - there are no pay increases for moving from neighbourhood policing to a county lines team for example. Pay rises are only if move up a pay scale due to time served, or are promoted.
Affairs are every bit as common as people think, but nothing in the OP makes me think this is more likely than that he’s just job-pissed. How long has he been in, OP?