As much as you like to lie to yourself that you've move on and you're cool that he has a new squeeze, don't or you'll end up asking yourself what if questions until you're 90.
Admit to it first, and then you can work on how to get him back! It might hurt you just seeing him around with his new girl, and chances are, it'll hurt even more if he calls you up and talk about her.
But instead of concentrating on his insensitivity, you should remember he called you up, that in itself shows how much he values you and your opinions.
Use that to your advantage.
Don't play around with that by bitching about his girl when it comes up in the conversation, rather, be nice and provide advice, and pretty soon he'll start comparing you to her and that's one way to get him back.
Once the friendship is established, and of course that involves casual nights out, don't make yourself too available.
We're not saying to reject his invites, rather choose it carefully.
Make a calendar if you must, but do fill those dates with actual activities so you have new stuff to regal him and make him feel like he's not a huge part of your life.
If he thinks you're pining for him, he might just peg you as desperate, but if you make it hard to get hold of you, the curiosity will literally drive him to distraction.
Relationships after a recent break-up usually tend to fall on the rebound category, so don't sweat it too much and stick to being noncommittal.
Keep your approach pleasant, and you're on your way to getting him back and causing his current girl to disappear from the picture.
No girl likes a guy distracted by an ex!