Hi there, lismarie79! Welcome to the forums!

I hope I don't sound too insensitive when I say that this is totally between your sister and her partner. You can be there for support of course, but there is pretty much nothing you can do to influence the stability (or lack of it) in your sister's relationship. And as hard as it is, sometimes we just have to watch the ones we love go through hard times in their lives (including their romantic relationships).

That said, I'm not sure I completely understand what your sister's issue is here...

If this is a jealous issue and if she doesn't trust her partner for some reason, that needs to be worked out between the two of them and they need to decide if they do have enough trust in each other to continue a relationship. Does she have a reason to doubt her partner? Have they talked about her feelings? etc

If she has a problem with the fact that her partner's ex is a man and not a woman (and thus maybe fears that her partner will want to go back to men instead of women?), then maybe your sis needs to be a little more secure in her relationship and open-minded and/or informed about bisexuality and realize that having had a sexual relationship with a man does not mean her partner is more into men than women or vice-versa. I think that for most bisexual individuals, it's more about the *person* than his or her gender. Just like with most heterosexual or homosexual individuals, falling in love is not based solely on the individuals gender, but many factors that make him or her attractive, desirable, and loveable. Know what I mean there?

The bottom line is that the past is the past, and your sister's partner has chosen to be with your sister in the present. It's no longer about this man in her past, it's about the woman she loves now.

You can be a support to your sister, as any sister would be. Buy her some chocolate ice cream and maybe hold her while she cries if need be. Give her a listening ear to turn to, but ultimately the best thing you can do for your sister is to encourage her to talk openly about her feelings with her partner.

Good luck to you and to her!

Angela