Most Helpful Guy
Girls love to think the next girl is just a rebound. So if it makes you feel good, keep telling yourself that.
The truth is, she might be, she might not be, either way YOU dumped HIM, so stop letting his actions and emotional well being intrude into your thoughts from day to day.
Most Helpful Girl
Its possible he's trying to make you jealous or just wants you to see how little you breaking up with him affects him (having already moved on). Although, you say he was already talking to this girl while you were with him which isn't a very good sign. Was this your reason for breaking up with him? If not, then then what was? Its understandable that you would be hurt by this. Yet the good news is its only a matter of time that he'll become sick of her and then guess what? His interest will fall back on you. Best thing you can do is move on with your life as well. And NOT to let him see or know how much his new coupling bothers you. The happier you seem without him, the more its going to bother him. Apparently, that's what he's done... and look what its done to you! I think by the time he gets done with her, you need to be over him and hopefully have your sights on someone who can give you the loyalty you deserve.