I have namechanged for this as I'm a regular. Please bear with me as this will be the first time I will have spoken about this in such detail and I want to get it all out. I was hoping that someone with a similar experience could help me with this as I think I'm going mad 
DP had a one night stand with a woman he had got friendly with in the pub (who was also a school mum) 3 years ago. We had been been going through some difficulties but I had no idea that things were as bad as he thought they were. This woman befriended him and was a "sympathetic ear" when he talked about some of the issues with one of our DC's who has ASD as she had some experience in this area. He said they only really talked about 4 or 5 times and the last time she made it clear that the house was empty as her DC's were away and invited him round. They were both drunk. I had a feeling that something was amiss and checked his phone, there was nothing immediatley worrying but in the drafts folder there were a lot of texts that he had started and messed up on the predictive to one person - a set of intials. Then I found one that said 'I don't know how I feel' so I knew that there was something to worry about. I called the number (it was very late at night) and her voicemail picked up giving her name, I recognised her voice as she has a different regional accent to us and I knew her from the school only in passing I confronted him and he denied anything had happenend and that they were just friends, blah blah blah. Over the next week or so we talked about it and I made it clear that such friendships were not on if I knew nothing about them and who the hell hides women's no's on their phone etc. I knew they had slept together but couldn't get him to admit it. I was on the point of taking the DC's to a hotel when I confided in a friend who works at the school that one of her DC's attended and she mentioned that the DC had told her that my DP had gone round their house to fix something. I knew then that I had caught him out on a lie and confronted him, as he said he had never been to her house. I told him I was going round to ask her what happened and he admitted that they had slept together once but they were both so pissed that it hadn't really 'worked'
I'm ashamed to say I went round her house to confront her. I was so mad at being made a fool of and lied to and this was a woman who knew my situ with with my SN DC and had been to our house to drop her DS for kids parties. She opened the door and slammed it when she saw it was me, but I tried to kick the door down. The only thing that stopped me was the fact that she lived near a police station. When I got back we had a long talk and he said he bitterly regretted it and didn't tell me the truth as he was ashamed and didn't want me to find out. He said he was distraught at what he had done to me and our DC's. He had also found out that she was really promuscuous and a bit of a lush so he was scared he had caught something and had run a mile when she had got in touch since. He offered to go but I didn't want to push them together and (in haste) told him to stay as I loved (love) him and didn't have my kids for them bring them up alone. I thought that I could get over it and that my children deserved to be with their father. I have confronted the OW since and she denied that anything happened, told me I was mad. She also called him and said I was mad and that nothing happened! He was amazed that she could be so self-deluded when he was there too but she was adamant. She did eventually say that she knew something had happened as she remembered him being in her bedroom. I made sure he got tested for STD's and also pointed out that she could have said he tried to rape her, as she clearly has issues with alcohol and memory.
One of our big problems was that we had zero social life as a couple. None of either of our familes wanted to look after our DC's, and we couldn't find a sitter so it meant that he would go out alone and leave me at home. Sometimes when DC1 was having an episode it was really tough and I felt bitter and let down. I explained this and the other issues that I had and since I found out he has arranged a regular babysitter so we go on date nights. If he goes out its for a couple of hours to watch football etc and never goes anywhere were he thinks she may be. He has really tried to make things better and is open about his phone etc.
My problem is that I am still so so angry. I hate her for deliberately targetting someone she knew had a disabled child and wanted to take him away from that child and our other little DC. If I could get away with it I would kill her and enjoy doing it. I know he has tried to make amends but sometimes when I look at him I want to punch him in the head and not stop. He could have ruined our DC's lives and for what? Some old skank that doesn't care what damage she does. It doesn't help that she is not some young glamourgirl, she is 12 years older than me.
We get along well most of the time but sometimes if we are arguing about something else, no matter how minor, I will throw it all back in his face and rage at him. The rational part of me understands how he got into the situation and that he has done everything to make amends but I can't help myself, it like I need to lash out. If he had deliberately set out to destroy me he couldn't have done a better job than this. When he does something lovely there is a little voice in my head telling me that he can't actually mean it as he cheated on me with an old rotter. I don't know how I can get out of this vicious circle and move on. We can't afford councilling and I don't think it would work as he will not talk about his feelings. We live in a large village and I feel that everyone must know about it an is laughing at me. I hate feeling so angry but I can't get out of it
I think one of the problems is that I have had no one to talk to. My best friend is angry with him to so is not the best person to talk to. I didn't want to confide in family as I want us to stay together and I thought that they would hate him for it. Someone else that I trusted was interested until she got some of the (edited) story then cold shouldered me when I could have done with her ear. Perhaps just writing this all down and having someone read it will help.