My (38M) partner (30F) has a healthy co-parentship, but BD avoids me. Any similar experiences?

My partner’s coparentship has come a long way since we got together. Early in our relationship, things were rocky. Her BD was asking to “get the family back together”, which created some friction between us.

Fast forward a few years and we have an ours baby and he is newly engaged. The four of us attend extracurriculars together, my partner is very friendly with his fiancé, and her and BD’s conversations have become short, to the point, and strictly about kid-related things. If things were like this from the start, it would be the model co-parentship.

Except for one thing: he consistently avoids me. He talks directly to her at those extracurriculars and doesn’t acknowledge my presence. When she’s FaceTiming SS, he’ll be Mr. Charismatic until I start talking to SS. His lack of comfort and disdain is pretty evident.

So, anyone else dealing with a similar situation? If so, how do you manage?