Is it ok for husband to comfort his wife in a sexual way when separated and living with another woman?

LONG story but feel a bit of background info is needed here:

My husband (37 & I'm 36) been together since we were 18, (I fell pregnant first time I had sex with anyone with our eldest child who just turned 17). Anyway, he left nearly 6 months ago saying he needed to sort head out. Found out three weeks later her slept with another woman (46), then found out that he had been with her up to a month before leaving the home.

Been together nearly 18 years, ups and downs like all marriages and truthfully over the past 12-18 months shut down emotionally due to him staying out drinking at least twice a week and coming home so intoxicated he wouldn't remember what he had said or done - drink driving on a number of occasions and not spending weekends with us as a family. (His bio father was killed by a drunk driver when he was young but husband does not remember him - his step-father, who he called dad died in 2010 after a 2 year battle with cancer).

I feel now we did need to separate to reignite the emotional intimacy between us but I never had the courage to actually do it (I was studying the past two years and we have 3 kids, 17, 5 and one with a disability 14yrs - life has it's challenges but felt, as we do love each other, everything would be ok).

I didn't think another woman would ever be involved in this (she had separated from her husband around 12 months ago now, has four children, two have already left home, younger two are 17 and 13).

I tried to shelter kids from the truth for as long as possible but about 8 weeks after he left, he introduced her as a friend - our eldest knew straight away this was a lie so we were honest and told her the truth. He moved from his mothers and in with her and in Jan moved into a new bigger home to accommodate the 5 children when our 3 visit (though our child with a disability hates him and it is a constant struggle in getting her to see him).

So, last week a family member of mine died and husband has been around to see me in regards to this (we were all the same age, and the death was unexpected). It has obviously upset me and brought up emotions that I'm sure hubby has thought about too.

In the days before funeral, he was hugging me while I cried and it was not like hugging a friend. If his new girlfriend knew or saw the way he hugged me she would not be happy as even I would view it as cheating (hands in inappropriate places...) As his wife, I didn't even think about her, though it has made me think since... The day after the funeral, he dropped off our youngest child and stayed for a few hours, again hugging but things went further and even though he said we should not do this, neither of us stopped it. We started to have intercourse, but stopped and kissed and hands were still not where they should be if we were not together until he did finish.

We both said sorry, but am not sure that I should be. He should for I feel he has betrayed his new girlfriend.

He had his phone off all week-end and we talked today regarding other stuff, and have not spoken about what happened on Friday, still acting as though we are separated. He has even said he wants our youngest to live with him one week on and one off, but up to the older two as to what they want to do. I said I do not think it is right to separate the siblings and really don't want my youngest to live with this other woman and her children one week on and one week off...

So, should I feel guilty about what happened between us? I do think it is a bit of karma for her as she knew he was married with three kids and slept with him a number of times before he left. Do I continue on as I have been with the separation and my own life, or do I hold onto the hope that maybe one day we can/do reunite? I know my husband would not tell her about it and I wouldn't as I'm not that kind of person (sometimes I think about it but know it would only cause trouble and sound like a crazy ex wanting her husband back. I'm not even sure that I do want him back after him cheating, as I always said it's a deal-breaker in our relationship! I don't even know if I want him back but sometimes think I've been with him for half my life, only man I've been with and because he is the father of my kids.

Thanks if you have read this and please feel free to ask questions for more info or comment on any aspect of this story as I appreciate the feedback...

SO CONFUSED!!!!