Dear Queenie,
I’ve been dating the guy who was my sister’s boyfriend years ago when they were in high school. Now she is married to someone else but she is all mifted about us being together.
Queenie, what’s her problem?—Puzzled sister
Dear Puzzled sister,
Some people (men as well as women) tend to be proprietary (and/or jealous or vindictive) about their exes. No matter that such people do not want to be with the ex anymore, they still do not want the ex to be really happy with anyone else, especially not a close relative who might bring the ex to family occasions, especially if the long-ago breakup was not on good terms.
Hopefully your sister will get over it. If not, it is her problem; do not let her make it yours.