He can like anyone he wants. That doesn't mean you have to like him back.
I think he can. It depends on the circumstances under which the relationship broke up.
yes he can because he might still want you
if you still like them and you guy broke up on good terms and you think there might still be something there then go for it...
forget about him
Well if you dont like your ex anymore then let them date. If you do still like your ex then tell your sister why you 2 broke up and ask her kindly not to date them.
It means that the reason that broke you up is still there. You or she are still doing the same behaviors.
you can tell if he looks at you in crowds or he says "he knows who likes you" something like that then yes. It also may depend on who broke up with who.
express your real feelings for him
of you broke up with him and you still like him then you obviously want to get back together. But if he broke up with you and you two are just friends then it is not that big of a deal.
if they broke up with you, move on. If you broke up with them and they flirt with you, flirt with them back
dont do anything, its not your choice who he likes
You learn from it, and move on yourself. It happens to all of us.
If you still have feelings for your ex, you can try talking to her about how you feel, but if she broke things off without telling you why, you will need to ask yourself i it worth going back to someone who would treat you that way.
it can be possible for an ex to still love you after a year of the break up...i know i still love my ex and its been about 2 years