Is it normal for you gf to get a crush on another guy? Ladies, if u can help?

Ok. I recently found out my girlfrien has this crush on another guy. For the past few weeks our relatioship was going downhill fast. We were constantly fighting, never huggin, or anything. ABout 3 weeks ago, she "broke up" with me but we got together because we both couldn't stay away from each other without breeaking down. Recentley, we've gotten things together and our relationship is on the way back to the top. But she said that a few weeks ago, she started liking this other guy, but as in a crush way. My cousin said "She may like him, but she LOVES you." I know this is true. And i know she won't ever cheat on me. But ladies, is it normal for you to get a crush on another guy while you're wit someone