You said the guy who's dating her is a jerk right ? Then don't think about him, be with the girl if that's what you want, and then if its meant to be she will want to be with you instead.
Nomatter what I really hope it all works out for you Henk (You too Njaco!)
What ever you do, DON'T EVER give up! Muster all you've got for this low period and get back out on the top!