How to deal with Jealousy in LDR?

I have a rough past and experienced someone cheating on me and it gave me trauma. My bf and I are both 23 years old. My bf now fiancé have coworker friends from a subsidiary company in a different country that he met one time during business trip. I know it’s inevitable to not have opposite sex friends. But I still feel uneasy because these coworkers (there one that’s aggressively chatting him and somewhat flirted with him during his business trip) are constantly keeping in contact with him on *** and send snaps to him. He replies neutral cuz he showed me their conversation one time. He told me too that he’s responding only when they chat first, to be respectful.

How do I deal with this? I know I shouldn’t feel jealousy I clearly know. I love him a lot and he loves me too. I know he loves me a lot because he travels 20+ hours just to be with me and it cost a lot but he still finds a way. But I still feel jealousy about this whole situation since in our 4 years together this is the only time it happened. it sucks cuz I’m having hard time to sleep these days from this stress.