How can I stop being jealous/paranoid?

Alex • 25, ABD&OB/GYN RDMS
So I've been cheated on and since then have experienced/ heard on and on about how men are dogs and cheaters and nasty. 
When my current BF goes out with friends I'm always consumed with the thought of what if there's girl with them? What if he's flirting? What if he thinks they're more beautiful than me? 
It's been an issue of mine for 2 years and it's very exhausting and sometimes I wish I didn't give a f***. About other girls around him. He's never cheated himself but I'm so scared since I have been cheated on before