[Always *]

I would find out the circumstances of why they broke up. See how upset he is about it.

The next thing to do would be to just be careful. Usually after a longer relationship like that people need more then a month to move on, so give her more time if need be, it'll also give this guy a chance to move on. Just spend time together casually and getting to know each other better.

You shouldn't have to worry about this guy, but I'd keep track of interactions with him and who ever his "crew" is so that if it does start going sour you can pursue legal action with evidence. But if he isn't pining over her and/or trying to get her back then it's probably ok.

It's a tough call, all I can think of is to give them both time to sort of get over the break up