its rotten, but as said hes your ex so you dont get to choose who he sees or how he spends his money
she is your friend and should be a bit more tactful, but i guess you now see shes not who you thought she was
are they in love?
also your seem to mention quite a bit about how you are skint and seem to resent them having money - sorry but neither of them are responsible for your financial situation, and neither should they hide the fact that they have a few quid...they owe you nothing....so on that issue yes you are over reacting.