ADHD Partner Has Ruined My Life

Hi I am new to this forum but have read many posts and can identify with many issues discussed.

I was with my undiagnosed ADHD partner for four and a half years and engaged for two.

From early in the relationship I knew something was wrong. I had never dealt with anyone like him. The tremendous anger outbursts over small things, short attention span, not able to communicate easily, never able to keep a job long or finish projects. But I was in a bad place when we got together and was glad of his other side, very loving, affectionate, would do anything for me and just made me feel like the most special girl in the world.

So I put up with the bad stuff. And there was a lot of it. I got sick and was eventually diagnosed with severe anxiety which I felt was possibly linked to his behaviour. I started to research heavily and made the link to adult ADHD. He ticked every box. I realised that we had to get him help or my condition would get worse. We saw a few doctors who unfortunately fobbed him off saying that only children have ADHD (very old fashioned views where I live apparently.) He lost interest after that and I wasn't strong enough to keep pushing him to look for a doctor that was actually willing to help. I could have left him I know but I loved him dearly and just wanted him to sort his problems out, and I'm sure many of you non ADHD partners can relate to this. 

Then, when I thought it couldn't get any worse, very recently my sister caught him trying to spy on her in the shower. I went numb with shock. He had alot of problems but no one thought he was capable of this. I just kept asking how he could do this to me (and her) and he told me he didn't know, it was a compulsion that developed recently and he couldn't control it. He told me he was addicted to porn (I knew he watched it and I wasn't happy, I just didn't know the extent) and at some point the lines between fantasy and reality got crossed. He swears he never cheated and to be honest we spent so much time together I don't know when he would have had the time. But I am not sure of anything anymore!

So I kicked him out that night. My heart is literally in pieces. I asked if he was in love with my sister. He says no, he loves me more than anything and only ever wanted to be with me. But then I say how could you do this? He said he didn't know, he just didn't think about the consequences and didn't realise how much damage it would do.

My sister is devastated. I am destroyed.  He is suicidal. I am very close to my sister and she is usually the one I talk to about all the bad stuff. She can't even bear to hear his name mentioned she is so upset by him. He has driven a wedge between us so now I have lost both what I thought was the love of my life and my best friend, and the relationship I had with my sister. I can't talk to anyone else, I begged my sister not to tell the rest of my family or friends because I am so embarrassed and ashamed. 

I am so depressed. I miss him, but not him the pervert, the him I thought I knew, my best friend. We were so close, how did I miss the warning signs? I don't know how to carry on my life is so empty now. How could he do this to me? He is getting help now apparently but I fear its too late for us because of what he's done and he didn't just involve me, but my sister too, and I am sure she will never forgive him even if I could. And my family is everything to me. His family do not help, they don't even think what he did was a big deal and I am overreacting. He thinks his dad has ADHD too, and his mum has many issues also, stemming from a violent upbringing. They seem to not care about anything he does and never have, hence why he did not get help as a child.

I posted on another add forum regarding this, and while there were a few understanding responses most were just horrified that I was suggesting adhd can cause someone to become a "sexual predator" (I'm not suggesting that at all - simply trying to understand his condition and the motivations behind his actions). I know ADHD can (not always) manifest such symptoms as hyper sexuality, porn addiction and difficulty in distinguishing between fantasy and reality. And of course impulse control issues. That's why I question whether I am being too hard on him because he really does have a serious condition. But there's only so much I can handle. I don't see a way round to be honest.

But I really did love him in spite of all his problems and I'm just so lost. How could he just destroy me and all we had with one thoughtless action? Can anyone help me make sense of things?