Need advice...

My partner is an avid runner and told me yesterday that he was planning on going on a run and asked if i wanted to go with him to walk (currently 7 months pregnant). I then said no and then he proceeded in telling me that his “friend” (that’s a woman) is going with him. I then had a conversation with him and let him know that this bothered me. He obviously “didn’t understand” why I am bothered and long story short, he’s still going through with it.

Am I crazy for having this bother me?