Just a vent, I guess...

If you're significant other has openly expressed feelings about an ex, unless you're in an open relationship or are polyamory, you need to nip that in the bud. I've never been the biggest fan of ultimatums, but sometimes they're necessary. If she can't 100% commit to a relationship with you, it's disrespectful, hurtful, and unfair to expect someone to tolerate it. If she's unwilling to do it, you need to end it, period. I know it's easy for us to armchair QB relationships like this when it's not our own feelings involved, but enough of us have been around the block enough times to know when it's time to take action and make hard personal life-changing decisions like this. We only say it because we know it's best in the long run.

If we truly loved someone but realized we are not right for them do we turn a switch off and no longer love them? Focus more on strengthening your bond and not the bond that they shared with another. they will slowly fade apart or you will realize you are also not compatible. If you are being proactive than you have nothing to worry about or regret.

If she admits that she is still in love with him, too, I think she needs to have a hard look at her own feelings and decide what she wants. Honestly, she probably isn't ready for another relationship if she can't let her past one go even after 6 months of dating you. It isn't fair for you to have to deal with that. I say you talk to her about it and decide what you both want to do.