That makes everything a lot easier. I'm 5'3 and I weigh 87 pounds when I'm a full grown adult. I feel bad for my boyfriend because he always says that if he has sex with me then I'll break in half and crumble into little pieces because I'm so tiny. Be THANKFUL your girlfriend won't break in...
5 minutes is okay. I mean, he'll get tired at some point. Usually in a good relationship it lasts 30 minutes though. Try to take some control next time and don't just lay there.
