I can imagine he has acted this way in relationships in the past, and perhaps it’s a part of why those relationships ended. Ask him if he can share more about what he gets from his relationships with his exes. With you approaching it from a place of curiosity, empathy, and craving a deeper knowledge of him, he might feel comfortable to look deeper and explain. Try to remember that, for whatever reason, for him, this was his normal before you two met. Why does he feel this need to be available when an ex calls? Perhaps he was once the one left alone — this could stem from abandonment by a primary attachment figure as a kid, a major death of a loved one, or even being ghosted by an ex. Then, consciously or unconsciously, he vowed not to cause that pain to anyone else. Although he could believe he’s just being loving, it could also mean he struggles with having healthy boundaries. It also could be about him feeling uniquely qualified to help his exes… Or, he’s just unable to say no because he doesn’t want to disappoint. Whatever the reason, you need to glean a better idea of why he’s doing this. Especially because you’ve said you believe he’s effectively choosing them over you. After some digging, you may find that, instead, he’s prioritizing his driving emotional need over you, not a particular ex.