My boyfriend cheated and still communicates with her

My boyfriend cheated on me with someone… I found out and he apologised. I later found out they were still communicating but he kept on with the excuse of being just friends. Afterwards I found out they were still having an affair. Settled and he said he cut all ties, unfollowed her on social media etc.

I have been telling him that I can’t even stand friendship with this girl. I later found out they started following each other again and she is back with calls.
I started complaining that this circle has played out one too many times. He said she just calls to check on him and I should deal with it that Mr A still calls you and I deal with it even if am not comfortable so I should deal with his.

(Mr A is a married friend that I got close to during a dark period and we have/had nothing going on.) Mr A mostly calls for business related issues which happens to be once In a while, but for some reasons my bf has never been comfortable cos he thought we had something going on.
Now he keeps saying I have issues and and making silly issues out of this. What I want to know is if I am wrong for not even wanting friendship between them? Am I insecure? Am I just being dramatic and making issues where there are none. Am I allowing my emotions control me?