One of my best friends was dating a guy and they had been dating for two years before they broke up, which is a fairly long term relationship especially for our age. They broke up about a year ago. I'm really close with my friend (we became friends a little over a year ago). I always knew the guy as an acquaintance and we saw each other often but we were never good friends. Now her ex has started talking to me. Not like flirting or anything - there's definitely nothing romantic - but just talking and being friendly. Obviously I've been 100% friendly to him but I'm questioning if I can really be friends with him and have my best friend be okay with it. I'm not sure what terms they ended on. My friend didn't want to talk about it when it happened and now it's been too long to bring it up. They're not friends now at all, but they don't go out of their way to make each other miserable. They just kind of cut all ties when they broke up. I'm not sure if she'd be okay with me being friends with her ex. They pretty much never cross paths, but it feels like if I don't tell her I'm going behind her back. However, if I do tell her, it feels like I'm turning it into a "thing" or blowing it up more than it has to be. Also, she never talks about him, so if I told her I would have to bring it up and it would be not only unnatural but it might look like I'm TRYING to start something. What do I do?

{Keywords (ignore): relationships, dating, ex, friendship, awkward, social, loyalty, betrayal, trust}