Any male advice on why my bf loses his erection?

Me and my bf have been together for almost two years now and for this time have had a happy relationship together. However i have felt that the sex has been a little bit of a problem... We dont do things very often and i would like to, it has always been like this so its not like it has just changed. The past couple of months when we have gone to do stuff, he has lost his erection half way through and at first i wasnt too bothered but it happens most times now and is starting to upset me and he knows this. I feel like im not attractive or he doesnt fancy me or like i dont do things right but he says its not that and he doesnt know what it is and says maybe hes concentraiting on me too much but i though blokes get turned on if they know they are pleasing their partner? Aanyway we got talking about this a few weeks ago and we ended up kinda breaking up as he said sometimes he wishes he was single so he can do what he want when he wants and when he goes out, not worry about what happens and stuff. I was really gutted but respected this however he still contacted me everyday saying he loves me and misses me and stuff and i felt like i was left hanging. Then last week he wanted to meet me for a chat and he told me he did stuff with a girl when he went out and how he feels awful and really regrets it and wants to get back with me...he was genuinly upset and crying and stuff and I was so upset as he had still been telling me he loves me and stuff. So anyway were giving things another go and the other night we went to do stuff and he lost his erection again....i thought things might be ok as he realised he does really want to be with me, i had even bought a little outfit to try help things and stuff. Just dont know what to think? any other blokes have this problem or do you know what may be causing him to lose it if he says he loves and fancies me and stuff? i think this is some of the reason he wanted to be single as well as he says he couldnt please me in that way. I know this is quite a long msg but if you have any advice it would be really appreciated thanks. x

Something, that helped me...

I met this girl 1 week ago when i was in Kiev, I called www.Gia.com.ua manager and arranged the meeting with Maya. She came on time, tidy and neat. Didn't speak too much and started from BJ (without condom as I like Then we made it doggystyle. After I cummed we talked a bit about life. she speaks good english by the way. Had some coffee break. then another one session , she was horse riding and cowgirl style. After I cum again I asked her to show me up Kiev (as we had one hour more), although it is not very safe walking in the center in the night - police are all around due to political situation and they always trying checking documents or asking money.. But it was ok that evening.

So generally I liked the meeting and the girl. She is quiet and nice, quite talkative and very passionate. I would recommend her.