So this guy i like and i have recently started talking and he did say he likes me and i really want it to work out. Like i already get along with his family and its really great

 BUT a few of my friends have said that he could be talking or just communicating with two others girls. Both of these girls have has their fair share of men and have somewhat of histories with the guy im talking to now. Just to add more confusion to the situation, my friends that told me this have a history of lying to me and have ruined previous relationships because of this lying they do. 

So heres my question, what should i do about it? Ask the guy whats hes doing if he is doing something? Im friends with his sister so i asked her and she said she knew nothing about it. I cant really confront the girls because they will start rumors (its a messed up friendship). I just dont want to jump to conclussions but its bothering me not knowing. HELP