Cheating on boyfriend.

Okay so we’ve been together for almost 4 years. I HAVE NOT CHEATED. & I probably never will. I was just wondering if it’s normal to get fed up and want to cheat? Like I know I won’t but when we’re arguing and things are going left I just think about it but it’s not like the thoughts make me feel better I feel worse because I don’t want too so I don’t know why I would think it.