Suggesting that you would cheat is extremely offensive.
I think what I'm trying to say is I don't think he is an abuser. I know that he has issues but he isn't a bad person.
I don't really think the label 'abuser' is necessarily helpful. Most "abusers" have a troubled past, insecurities, often toxic or abusive parents. That's why they became abusive. They don't intend to be abusive or to be a bad person. That is half the problem of dealing with them: they simply refuse to believe that the problem is them not you, they genuinely believe that you should tolerate their behaviour. It is justified. Every apology will come with a justification, a reason that it is not their fault, a reason why they could not help themselves, a reason why you are overreacting, a reason why it was actually your fault that they behaved badly.
Many people confuse understanding why a person is badly behaved with accepting the bad behaviour. You can understand without accepting. Sometimes that means walking away.
He wasn't always like this. We've been together 14 years. Am I kidding myself that we can resolve this?
I certainly think that Relate is a non-starter. The problem here is with his behaviour. This is not a matter of compromise. It is a matter of him sorting out the mental health problems that result in mis-treating you.
Has he taken any moves, of his own volition, to get treatment for his inability to cope with you voicing a negative opinion, for his troubled relationship with his mother, for his deep insecurities? Who decided to go to Relate and made the appointment? What solutions has he offered?
If he desperately wanted to change, then he would have sought the help to do so. He hasn't. That says it all. You aren't worth it.
Despite all that, however, to me, the most important thing you wrote is I dont want to live like this.
So don't. It really is that simple.