I would like relationship advice?

I have been with this guy for about 8 months now, we started dating about a month after i moved to this town, and i thought he was the best guy i have ever met. But now i'm not really sure. He's always talking to other girls and hanging out with them instead of me, and i'm not sure if i trust him anymore...I also logged onto facebook today and he's been being tagged in a lot of pictures (most with girls) and the first thing i saw when i logged on was a picture of him next to some chick (Hailey) and he was making comments about how she looks good, and how he loves some other girl more than Hailey does...and when i saw that it killed me, even though i know he's probably just kidding around it still hurts to see that...what should i do? How do i tell him that the way he acts with other girls isn't okay?