I am 20 years old and my girlfriend will turn 20 this wednesday.
I think about her all the time. We have a near perfect relationship. She will spend full weekends at my house and we will sometimes talk for 30 hours straight. We are in great physical shape, attractive, and are both very much in love. We both have had relationship problems in the past, my ex-girlfriend who I cared for deeply left me two years ago, and her ex-boyfriend was nothing short of a douchebag to her. I can't express to you how happy we are together, but we decided to take it slow and we only recently (2 months ago) started to have sex. Let me explain what has happened everytime.
We have a great beautiful and sexy buildup and we are both very "into it", then only a minute after I've entered her she begins to cry and stops me from continuing. When she was drunk she explained it to me, she said that she starts to worry that she won't be wet enough, then she can't be into it so she loses it and feels inadequate.
This happens almost everytime and I spend the next half hour telling her that sex isn't that important to me, I'd much rather just lay with her than make herself feel bad. The only problem is that when she tells me she wants to try again its too much of an expectation and is too "built up" (my words, not hers) so the same problem happens again only almost worse.

Please help me, I'm so terribly in love with this girl and want us to be happy.
Thank you