How much do you ask about their exes?

Well don't just come out and ask "is that weird that you broke up?"...You can get a more explicit answer if you say "Is that a good thing or a bad thing?"...I wouldn't just randomly ask a guy about his ex though unless they bring it up first or if they continuously talk about them (In that case, I would think something is up)

I don't think it's weird to ask, but if he gets touchy about it I'd back off until he was okay to talk to you about it. I'm not suggesting that this is the case with you, but just in case this comes up I thought I'd add my $0.02.

For me and my SO's, until we start dating exclusively and we aren't already friends (in which case I'd most likely already know his relationship past) I follow the Backstreet rule.

I don't care who you are, where you're from, what you did, as long as you love me ;)