How should I deal with my roomate?

I share the house with 4 guys. Two of whom are problematic gamblers. I invited my GF to sleep over for a few months. One of the gamblers accused my GF of stealing his rent money. I think its more likely that the other gambler is going around scrounging for money cuz he doens't work at all. My GF is at my side all the time so its definitely not her.