I'm having some insecurity issues with my friend whom I am in a casual
relationship with constantly being with his ex-girlfriend. He's been my really close friend for the past 4 years during which he's had 2 relationships with other girls. In the middle of the 2 relationships, we decided to move to a casual relationship. He began dating 3 months after and we broke it off. It's been a year since he broke up with his last girlfriend and we've been in another casual relationship for over a year now. We've been in secrecy so that it does not affect our relationship. However, he's constantly with his ex and they meet each other all the time. Although I'm convinced he won't get back with her, his behavior and closeness to her is bothering me. He doesn't reply for hours on his phone when he is with her and gets very insecure when I talk to other guys. Unlike other casual relationships, I cannot simply forget about him because he's my best friend. Please help!