Arginine is a pro-viral so...

There probably isn't much you can do to stop this. I'm amazed you can last as long as you do. I remember having a permanent boner around my girl.
However, to slow it down, there is desensitizing cream sold at the drugstore. You could rub some on just before you go to make out. Be careful where you let the sperm fly...it is possible for live sperm to migrate into her vagina. Even thru underwear. But probably not likely.
If it still happens, wait a bit and go for round two.
Remember, as with any date, communicate how you feel to her. You should not be embarassed about something that happens normally.When it does happen, continue with foreplay on her...you will come right back. You are near or at your sexual peak...enjoy it...your normal! It only gets better as time goes on.