[Raziel]

I'd go around him completely & tell her to back off.

Perhaps she is not aware that he's in a relationship but it seems like a stretch.

Another thing I'd do is check phones - it's a gamble but there are some warning signs here.

Emotional etiquette is not being respected by either of them & as you have already pointed out - he was quick enough to insist on some assurances, why can he not give the same back?

His first love is essentially the one that got away - screw whatever closure they have to work out it's long done.

You deserve some respect.