Need help!

Me and my ex, still like each other, but it's hard for us to get back together, anyway, when she's in her school shirt my male friends like to look at her chest and i don't want to look at her in that way! What can i do???

Why are you worried about it, you are not together anymore. IMO, they can look at her in any way they wish. Just because they look at her that way does not mean you have to. You cannot control what others say and do, the only person you have control of is yourself. If you don't like what they are doing, go into another room.