So my daughters father left around a month ago
We were arguing too much and needed a break from each other and it wasn't healthy to have that around our child .
He came back for a night and told me he loves me, wants to be a family, and I told him the same . He's the only one that has really taken the time to understand me all these years as much as I've devalued him in the past he has been here on and off just leaves when I get worked up or we fight because our child didn't need to see that .
The day after he said he wanted to be a family he was going to pick me up from work but didn't , he called me and had drank too much. I got so upset I felt abandoned and let down . I ignored his text for three days and got a babysitter. I ended up drinking too much and then ended up sleeping with our mutual "friend"
My SO finds out. I was too afraid to tell him . I really made the wrong choice in the moment I was upset , out of control, emotional, lonely lost sad. The friend knew this and knew I have been ill but still did it. And had done this 2 years before that . All of which I hid from SO . But now he knows everything and says he isn't a sucker and can't deal wth the deciet. I told him I'm sick which is true and I'm a mess , starting DBT therapy this week and I begged and promised I would make things right And get well so we can be a family. He says he can't overloook what i did. I am filled with guilt, ashamed , disgusted with myself and wondering how I could let my emotions let me do this and lose control like that. The real me wouldn't have done that I keep trying to explain to him . I want nothing more for him to forgive me but I understand how impossible that is. Where do we go from here ? I want this man in my life he is the only one who makes sense to me and has been there for me in the ugliest times. I know what I've done is horribly wrong. I rarely drink either not that it's an excuse it just made me so emotional. And reactive. And I felt so abandoned by him even though I knew eventually he would come back home to us. He's not a bad person but my disorder makes me think he is sometimes . Is the whole thing hopeless? I didn't mean to be deceitful or manipulative I just didn't want to tell him because I knew he would leave me 
I've been spiralling downward for many years now and I just hope therapy and meds can help in some way. I'm not excusing my behaviour it was disgusting and I wish I could take it all back I feel repulsive 