Words from the bottom of my heart (might not sweet to hear):
If she is very happy with her current life/bf, you may think that you really couldn't satisfied her when she with you together, thus you may feel sad.
If she is unhappy with her current life/bf, you may feel mercy on her even you don't want to 返o卓 and try to give her a better life (now is the case).
In any case, you may feel sad anyways. So, why bother my brother?