Sounds like you are setting yourself up for a lifetime of heartache and anxiety, he hasn’t treated you very well in the time you’ve been together, the behaviour you’ve described doesn’t make it sound likely he will change either.
you say you’ve invested a lot in the relationship but that investment sounds one sided. He hasn’t made you a priority at all, ever. And by continuing to accept his behaviour, he will never have to either as he knows you’ll put up with him no matter what.
I don’t have much experience (one serious relationship of 20yrs from a young age) but I can tell you that now I am out of that relationship- as hard as it was to accept, and how awful it felt at the time - I now cannot believe the utter shite I allowed myself to put up with! And I can say I will never allow that again
it wasn’t easy to get over, and early days I thought about how we could get over his affair, it would have been the easy option to forgive and forget and take him back, but I know in my heart that would not have worked long term. We would have both been unhappy in the long run.
i don’t think it’s impossible to get over and work through in some circumstances, people have done it, but usually have a much longer relationship and commitments that make it seem worth staying together
i I don’t think that would work in your case. He’s never respected you or your feelings. He’s unlikely to change that now.
you have no commitments to him arrant staying together - no children/mortgage etc. you are actually in a great position to walk away and never look back
find someone who chooses you, who loves you, and shows it. Believe actions, not words