If hearing about his personal problems with his wife feels uncomfortable to you, it feels uncomfortable.
As for guessing why
it makes you uncomfortable (really only you know...)
What's is your need from BF? Could take a need inventory
to see if that helps you articulate it to yourself.
Is it that you are ok hearing him with wife problems because you know your own place in his life is secure? But then hearing how much he wants connection with her is perceived as "going toward her and away from me" so that's putting you on shaky ground emotionally? You don't like talking about emotional subjects or emotional intimacy? Something else? (I could be guessing wrong. )
i felt these were intimate details that made me feel like he were talking to a buddy instead of his girlfriend.
A GF is not also a friend?
Or is it that you are relatively new GF and this is getting too heavy too fast?