Shared Son

Primero has been spending a lot of time with his friend's family. It's something a lot of teens do but, in addition to my concerns about the age difference between him and his friend (she will be 15 the end of this month), I have also discovered he calls her mother "mom." I've actually heard him do it, just before he put me on a video chat with her. I think he thinks it's a gag. Only, when I talked to her (she does not speak English and Primero speaks only a little Spanish), she jokingly said he wasn't just my son but that we shared him. He was "our" son. I guess for ordinary people, this would be just a silly joke, haha what a lark. But, for me, it does not feel that way. It gutted me to hear him call her mom, to refer to her as "Mom" to his friend. Our family therapist suggested I try talking to him about it but I just can't. The pain from the past makes me feel too fragile to bring this up as something that bothers me. To be honest, I just couldn't take him acting like it's nothing, like I'm an idiot for feeling some type of way about it. He wants me to be friends with his friends mom, but I have thus far avoided meeting her. It isn't her fault, but when she said he was her son too, I just couldn't stomach sitting in front of her and acting like I was totally cool with that. Maybe I am an idiot. Maybe I am jealous. Maybe I just feel like I've worked so hard to earn the title she was given so freely. Primero has lived with me for five and a half years. He has been adopted for nearly three years. And yet, he still introduces me as his adoptive mom and never, not once, has he called me "Mom." He met this woman like three months ago and she get's called "Mom." What's not to love about that?