Am I being unreasonable ?

Ok so my SO has the female friend and he use to have feeling at first they really wasn’t talking a lot but now they’re talking more than that’s usual like texting more and talking on the phone so I told my SO that I’m uncomfortable with him talking with someone he had feelings for because I’m scared the he’ll develop feelings for her again he says he doesn’t have any feelings for her anymore and he really doesn’t want to stop talking to her because they are really good friends so I wanted to know am I being unreasonable?