Can't cum during sex (female)

So my boyfriend an I have been sleeping together for a little under 2 months now and I can't seem to finish with him. I have been with 5 guys total and have never had this problem in the 7 years I've been sexually active. I'm able to be extremely turned on by him and get to the very edge but then I just lose it. He also is sorta a minute man but we try to work around it, stopping when he gets close. The only time I've been able to cum with him is after about 6 blowjobs and then we have sex (he was incapable of cumming at that point lol). Now I've read a few other forums about trust issues and being open with my partner and things like that. The very first time he and I fooled around I physically showed him what to do, I took his hand with mine. And I have no trust issues with him, no bad sexual history. My question is can anyone think of a way to help him improve, or help me relax? he's only been with 2 others prior to me. I'm 21 with a 1 yr old son (dunno if that would make a difference) and he's 23... I'm not loose at all, when I masterbate I'm still tight enough that he sometimes complains about it. :p difficulty getting in.