Husband to be allows ex to have account in his name

My soon to be husband's ex wife still has his name as the acct primary on her cell 4 yrs after divorce so she gets to benefit from a military discount of $12/month. (Yet its OK for me to pay full price for both of us.) Their 16 yr old has a minimal usage cell on her acct. My partner wants to join my cell account and I offered putting the son's cell on my plan so his ex can remove any financial accounts in his name - and puttin it in her name. Four years of benefitting from his occupation and now we are getting married and he doesn't see where financial absolution from her is moral, ethical, financially responsible. I think he can't let that one thing go because his guilt from the divorce stills remains. But, I can't share my husband. I've been
Divorced two years now - after 10 yers of marriage - and it wasn't easy to move on but we did. Should I stay or go?