someone give me some advice PLEASE!!!

I'm kinda curious as to what the hell is wrong with me. i think i may have ED??  i can achieve an erection just fine and if I'm by myself and I'm masturbating i don't have a problem, but when i get intimate with a girl, a lot of times i cant seem to keep an erection. i don't really understand why it is intermittent problem. please someone help me out???

[SixStringer]

A lot of sex has to do with psychology.  Due to distracting thoughts when you are with someone, your "plumbing" does not always cooperate.  You may not always be conscious of specific thoughts, but in the back of your mind it could be many things such as possible pregnancy, satisfying your girlfriend, getting found out, "performing" properly, bills, school, and so on.  Just worrying if you can "get it up" might make it come true.