I think my boyfriends best friend is a bad influence..what should I do?

I've heard quite a few times that if a husbands friend is having an affair, that he is more likely to have an affair too because he thinks that since his friend is doing it, that he can get away with it too. I've been dating my boyfriend for about 2 years now and we have some rough times but we get over it. But lately he's been acting like he wants to be single. And I'm almost 100% positive it's because his best friend just got over a relationship and has been fooling around with other girls without any consequences. I'm worried because I don't want him to want to break up with me just to be able to fool around with other girls and have freedom. I don't know what to do because every time I try to let him have space he says I'm being distant, but then when I stop giving him space he acts like I'm suffocating him. I need advice, I love him so much and I don't want to lose him due to him wanting freedom like his friend..If you say 'just talk to him' please help me figure out what to say because I'm not sure what or how I should bring it up..please help