Honestly, I would sit down and talk to her about your relationship. Do you guys need more consensual boundaries? Could there be an aspect of the relationship you guys need to work on? Or is it simply she needs time and a break to sort out her feelings? That's the time to ask the hard questions. This is purely me and not for everyone, but when something similar happened with my wife (then gf) we talked all night about what it was we both needed. I soon realized for a month she'd been in a place where she loved two people and loving someone else didn't mean she loved me any less. So I met the woman and immediately understood the attraction. She was a smart, bright, and cute person. We talked like adults and found a solution. Eventually, feelings subsided when my then gf had the freedom to explore them and we came out stronger than ever. She proposed to me and we've been married 3 yrs ago. For me, love isn't about keeping someone all for yourself, it's about wanting them to be happy. If she had found more happiness with her crush, I would have wanted that for her. Besides, would I have wanted to be with someone who felt torn by staying?