Put this whole man in the bin.
Honestly, he's not nice. And that's all you need to know. Regardless of any shortcomings you may or may not have, regardless of his friend. This man is not nice.
He does not hold your best interests at heart or act on them.
He is damaging you and he is not nice.
The very least someone should accept in a partner is that they are nice. If they don't have this, nothing they have beyond that is worth half a shiny shit.
Don't worry about keeping things amicable because you will still see him around. He doesn't deserve your kindness now and he won't when you bump into him at Tesco or the pub.
Gather up all the strength in your titties and tell him:
"Douchebag*,
I've given time and consideration to our relationship. I've invested in it emotionally and financially in the way of private therapy.
However, I've come to the conclusion that no amount of effort can balance the scales with you being just awful.
You, from day one, have attempted to establish a insecurity in me and then manipulated me in such a way to make me believe I was the person with an issue. I am not. There is something terribly wrong with you.
Your friendship with Douchebagsfriend* is something you should consider, along side your general nastiness before venturing into another relationship.
In case you missed it, you're now single. Enjoy. Or don't. But definitely work on yourself.
Byebitch."
*Might want to change these names, might not.
But honestly, my love, you're worth more than this.
In.
The.
Bin.