Could not trusting ppl hurt you............?

No one really likes me and I only have one good friend that I've known like all my life..and aquaintances...alot of ppl give me a hard time at school and I'm really hesistant to let ppl in especially guys...they're usually really mean to me, and when a guy is nice to me I think it's all an act....if a guy says hi to me or compliments me I don't really respond because I figure someone probably dared them to talk to me or they could be being sarcastic....and there's this one guy that always tries to talk to me...and he's always really nice.. but I try not to let him get close because I feel he could just be playing around because I don't see why a guy like him would talk to me...he could have anybody he wants.....everytime I see him coming I just walk away or if he comes up to me I keep the convo brief and make up an excuse to leave...and if he asks me to go somewhere with him I say no because I figure he might just be playing and not even show up...he found me on myspace.. (that's the only time I really talk to him) and I was telling him how I write poems and stuff and he said " could you write one for me gorgeous" and I didn't respond. He told my friend to ask me why I always seem so distant and why I act like he's gonna hurt me....I'm trying to spare myself the heartache of being screwed over or getting my hopes up,but my sister says if I don't ever trust anyone I'm hurting myself... I just don't see why a cute popular guy that has lots of pretty girls chasing him would look at me when most guys treat me like crap...I have to wonder if it's a joke....should I really give him a chance??