Am I being Rational ??

So I have this ex best mate. Recently I found out that she has become friends with 1 of my best mates. Is it bad that I’m uncomfortable with them being friends bearing in mind she took all of my friends away from me and I had to try really hard to get them all back.

I’m just scared that she will either date him and break his heart or just take him away from me completely and turn him against me. I’m probably just paranoid but should I tell him how I feel ??