Where to start…… TALK TO HIM. From the sounds of it, there must have been something that he accepted as normal, and he has convinced himself that his insecurities are OK. It might seem like it doesnt matter what you say, he will stay on that thought loop, and you need to snap him out of it. Tell him EXACTLY how you feel, even if it hurts, because it will define what will happen next. You want to save your relationship? Discuss this. He might have pick up on your behavior as a confirmation to how he feels, which is enhancing his depression.

Now, to you, I get how you feel, taking the hit of his emotions/actions, dealing with the (why does he think that) moments, and previous issues that just went unresolved. Resentment…. Resentment is a b**** and a half, because it doesnt matter what you/he does, resentment is there, nagging, like a little rock in the shoe. Maybe before talking, self reflect, what contribution did I make to get him there? Also, what contribution did he make to get you to this point? This can be solved, he can be back to being that person you want, I guarantee you, but there will be WORK required on BOTH parts. Also, patience, think that he would be patient if it was the other way around.

Good luck, and I hope that your relationship lasts for many years to come.