My two best friends like eachother?

First of all I think you need to ask yourself if by any means there could be a chance that you might like your guy friend, dont anwer quickly, actually sit back and think about it. Because you wouldnt have to think about letting him live his life if there was a chance that you might like him and maybe that is why you are worried that it could ruin your friendship. Your girl friend on the other hand needs to finish her current relationship with her own boyfriend before she can actually start something new. If she doesnt then they will get you involved. I say once you settle your own feelings for him you need to talk to him, since you have known him the longest, and i bet it would hurt you more to lose him then your new friend. Just let him know what is going on, get him to tell you how he feels, and then go from there. Hopefully i helped more than confuse you more lol good luck!!