Thank you for replying.
I don't really post, I'm a lurker!
Jeez, I don't know where to start with a backstory to this. Before I go any further though I need to point out that I know I should have ended things long ago, it was just so, so hard and I felt (and feel) under intense emotional pressure from H, and he has this knack of making me feel responsible for his actions (ie it's all MY fault) and to feel bad about circumstances he has now found himself in, again with the guilt and feeling sorry for him.
H has depression as a result of childhood/family issues, previous drug addiction (opiates) in his teens/early 20's and more recently addiction to painkillers (codeine) which he is now receiving treatment for (methadone).
I have tried to be suportive of this, both the mental health issues and the recovery from addiction but I have failed miserably because frankly, I just don't care enough, due to the way he has behaved in our relationship prior to the painkiller addiction.
When our 3rd child was about 6 weeks old H started looking at those online adult contact sites. This quickly progressed to daily usage, when I confronted him he denied it. He then took out a subscription, I confronted him, again he denied it. He said he was trying to delete his account/profile but didn't know how 
I checked for myself, I was able to register and deregister all witin 10 minutes. Still this was beyond him. He even started to come home at lunchtime to log in to the damn thing and I'm there like an idiot trying to look 3 DC aged 3 and under. I told him I didn't want him anymore, I wasn't prepared to be treated this way and started to make arangements to leave. He deleted the account straight away. However, he had already exchanged e-mail addresses with women he'd met online.
I forgot to say that his reasons for all this were mostly due to lack of sex with me and attention from me. Okay, I hold my hands up to this, I really did not want to have sex within weeks of a 3rd C-Section. So definately my fault
We tried to make things work after this but for me the trust was broken, and when we had sex thats all it was for me, just sex it no longer felt personal or intimate 
Fast forward to about 6 months later, I am making plans in my head and talking to my closest friends about leaving and how best to do this. I found out H was viewing porn on laptop. I wasn't too bothered at first until I looked closer and it was the "Teen" stuff which I just think is fucking horrific and so so wrong on every level. I confronted him, he denied it! I showed him the evidence on the computer, again he denied it! He then started using adult contact sites again, progressing to arranging to meet up with people. All just the final nail in the coffin for me.
I made my plans, I kept him informed regarding the DCs. I left my job which I loved, said goodbye to my friends and moved away. So for about 3 weeks I was on my own with my lovely DC and it was the best 3 weeks of my life! Then H turned up, said he loved me so much, couldn't live without me and the DC, etc etc etc. I so STUPIDLY let him stay and everything just went downhill rapidly. We haven't had sex for well over a year, and recently he wouldn't be able to anyway because of his medication but he kept talking about when he has recovered and I just felt sick at the thought and when he touches me, even in passing, my skin crawls.
And today I asked him to leave. He has gone to his mothers about 200 miles away.Said he can only stay there for one night and then will have nowhere else to go. Our house has gone now so he can't stay there.
I don't want him back. I don't want to be with him. But I do feel guilty for some reason an kind of sorry for him, and also a bit scared and apprehensive.
I am sorry about this post, I started off intending it to be something very different from what it has become.