Guys: when dry-humping, how can your girl prevent the pain?

I have a boyfriend whom I have been with for almost 3 months now and we've made out a bunch of times and I already gave him a handjob. But im thinking about spicing things up and I was considering dry-sex/humping (w.e you want to call it xD) but I've...

heard that guys pen!ses hurt sometimes while having dry-sex and im scared that while we're doing it he'll be in pain and/or not enjoy it. What causes this pain? and what can I do to prevent it and make it enjoyable for him too?

--Yes I'm 14, almost fifteen so don't say anything like "oh your too young STOP!"
No moms please :]
--I know what I'm doing and I will NOT give up my virginity at this age yet..

I don't know how it hurts... watch his b+lls!

Don't worry. If it hurts him, he'll stop.

The pain is caused by friction, but only if he's moving his pen!s a lot. If the humping is more like a gentle rubbing or squeezing action, he might be ok.

If he wears a condom, he can put some lubricant in it to keep himself moist. Use KY or a water-based lube, not vaseline or hand-cream.