<human>: Could you distill the essence of the text into 1-3 sentences?

I have exams & my mind is constantly bombarded with distracting thoughts of an affair my bf had a few months ago. 

We started dating a year ago (btw, age:both 22) from today and it lasted for two months before he had to go away to another country. The long distance thing lasted for some 8 months. During this long distance thing my boyfriend would talk to me asking if I was willing to consider this relationship open (we had no idea at first when he might be back...). After much debate I said something along the lines of:  I would be O.K  with a sort of one night stand thing but would be very upset if he ended up having a relationship with another lover...Stupid me 'cause a month before he comes back ( and at this point he knows hes coming back in a month and has reserved a ticket), he ends up in an emotional/ sexual relationship with a 40 something year old woman, who is ill, divorced and has a child. 

He talks to me about it -we fight, I tell him it hurts me, he tells me he is in love and understands that I am hurt but this force he is experiencing is too powerful being with her is spiritual freeing etc....

Somehow we manage to get over this and get back together. At first it was a struggle, then he starts to tell me that he is beginning to feel closer to me and feels himself letting go...The relationship has been going very smoothly, but I get thoughts, disgusting vexing  thoughts of them having wild sex and it makes me want to puke. I can't do this anymore, I just want to run away, but he's being the most caring loving person I've ever known. 

What the fuck do I do ? I can't seem to get over this, It's been 3 months since the incident. Should I have left before when this affair happened?
<bot>: An affair my boyfriend had a while ago while we went long distance still has powerful negative effects on my emotions towards him. I can't seem to get over it. What do I do?