I found much comfort in your comments!

Unfortunately, he is still looking for a new therapist.
Of course my interpretation about the divorce is just a guess. But his mother views it quiet similar. I think he is looking for romantic love to be something that is as absolute like the love parents have for their children. This is why he wants his partner to be everything and to be around all the time, to count on always! He is very hesitant to open up...and many things about my past just violate his idea of love. It is eating him alive.
This is why he is always expecting the worst... he wants to regain trust. But is afraid to be disappointed once more... I sense this and am afraid to disappoint him... and it pushes me to make one "mistake" after another.

Today things escalated. I hope it is for the better. Don't know though... When I finished work I had a text from him saying that he was really sorry but he was in a bad state and didn't want to put me throug this... When I called he sounded even worse then the last time when he was saying things like "I don't want to be me anymore..."
He said he doesn't know weither he should go to the psychiatric clinic... he had read some girls personal report about a threesome...
I was asking him to go to his parents or to a friend or to let take him to the hospital. He said he had nobody to turn to and that he is going to end the call and hang up.
I had about 5% battery left on my phone and couldn't reach his brother. So I went to his best friend so that he could have a look. And I texted his brother what he had said... who called their parents. When I had come to my senses and called his parents the were on the way... called a doctor... tonight he is in the hospital.

His mother was a mess when I came to his flat... (jaust for today he had told me to take the key...)
I love his parents. It was a comfort to see them.

I was just texting with him... this doesn't make sense anymore. He was writing how much he loves me, that he wished it was my snoring next him, not some stranger and then his thoughts returned to the threesome...
And he started asking how I got in touch with his best friend, why I knew his last name and where he lived... (and I can guess what he might imagine...)

I really don't know. I can't do this anymore. I want to be there and support, but either he realizes that there is much more to this and that his insecurities don't route in my past... or I just can't take the responsibility for his state...
His father said something like: "He should be glad he got a pretty girl, instead he is putting you through so much." And that his son is always trying to make everything perfect...
This reminded me of some comments here that comforted me so much and make me feel I am starting to get back to my senses.

When I came back to my parents they were crying. My mother fears her cancer is coming back...