My Uncle, Minden, has two sons.
One son, Ryan, is smart, dedicated, and loving. But he suffers from anxiety to the point of being crippled in a lot of jobs. His girlfriend has been with him for years and loves all of him. She works with his OCD, his anxiety, and has helped him complete college, get a job, start good hobbies. And it works for her, because he does not use his OCD/anxiety as an excuse.
For Miranda, the 30% anxiety/OCD is outweighed by the 70% good. She feels loved and taken care of and their personalities go well together.
The second son, Joel, has never had a relationship last more than two weeks. He has too many mental issues to be with someone else. He cannot take care of himself, lashes out, and blames women for his own personality issues. He has lost a relationship with Ryan because he calls Miranda a slut. He has ranted about how Ryan is stupid and should not have a girlfriend when Joel is alone.
You have to decide if you are dating a Ryan or a Joel.
Would you leave your significant other of four years if they are controlling and possessive, even though they have good reason for being that way and are working hard to try not to be that way towards you?
I would leave if the situation did not fix itself within six months. I understand you have put a lot of work into this. You seem afraid of being alone, but this guy is going to make you far more lonely than being single would.
When you only have one person in your life as your everything then it starts a weird power struggle. You feel like you can't leave because he has all the things you need. You have turned him into your social, romantic, and familial life. And that is unhealthy.
It is fine to be close with your partner, but if they drive away everyone else you love, then it is not healthy.
I have left guys who had issues like you described. I shouldn't have to tell someone to treat me with respect or stop controlling me. And some people shouldn't be in romantic relationships.
Everyone has strengths. Some people make terrible boyfriends, but great friends. Some people are terrible partners but great at parenting. You might think the world of him, but if he has not improved in 4 years then maybe he needs to be single to fix his issues.
Do you cut your losses and brave your fear of being alone or do you try to push through this obstacle that's been present since the very beginning of the relationship?
These are not new obsticles. They are the same ones.
So I would leave.