lucky, *shakes head* i had the SAME problem. Im probably younger then you, im 24, and all means i am not lacking sexual expierence either. Like i said i had the same problem, actually my first thread on the library (under another name) was about this same thing. Everyone told me 'oh you need to relax' it wasnt about relaxing! I was SOOO comfortable/ relaxed with my exgirlfriend and boyfriends it wasnt even funny, but i still couldnt cum from sex or from them going down on me, or fingering me. Id get REALLY REALLLLLLY close but nothing..
I would masturbate for HOURS i mean HOURS with different toys, positions, porn, thoughts, cybering and NOTHING would work. Nothing. Then you get the mass amount of peole CLAIMING they can make you cum, lol like a god damn free for all.
I even went to my GYN and asked if something was wrong with me. She said nope.
I finally came just though, not through sex though. i dont know whats different about this relationship, im no more comfortable with them then i was with anyone else. I guess it just happeens when it happenes.
since i have been in your shoes, all the advice you are gunna get MAY help you, but it didnt help me. I just waited it out, didnt think about it to much when it was happening, and just let it happen.
So good luck!
ps. i STILL cannot cum from sex, alone. There has to be other stimluation going on. Im not gunna push the 'cum with sex' issue bc maybe itll never happen for me, idk. either way, i lived without it for 10 years now i think i wait longer lol