First, it’s important to identify if it real love or your brains playing tricks on you. Because it’s human nature to have desires, crushes and even fall in love with other people during the time of being in a serious relationship.
At times people in serious relationships will leave their current partner for something that they deemed as love, and eventually find it was the worst mistake of their lives, thus ruining years of a happy marriage, family life, stability etc for the thrill of love and excitement. They may come back begging for years by trying to get back with the person they took for granted. So this is a fine line, and unless I know 100% that the person I’m with is wrong for me and I’m not in love with them, I would think twice before leaving.