I think if it bothers you, you would have the right to squash this, it's a conflict of interest for your therapist. Two acquaintances of mine see the same therapist, when my therapist found out that I knew them she made sure I was OK with things. I'm not sure how she would have dealt with things if I wasn't OK with the situation, but it was nice that she at least asked me about my feelings.

Seems you have mixed feelings about the situation, I would talk to your therapist about it, maybe you two can work out some arrangement that will ease your mind.