Keep thinking bad thoughts

Been with my partner for a very long time. Recently I've began to "crush" on a co worker. Who I can honestly say reminds me a lot of my SO. No I have not done anything bad just baby flirts (I don't even know his last name) nothing to cause concern. The issue in having is I keep thinking of and having dreams of us having sex/kissing. I've been having these feelings for a few weeks now and it bugs me because I love my SO so much. I had someone tell me that they noticed the "thing" between us and that it probably won't go away unless something is done about it (like acting on it which I don't want to do). Help. Has anyone else had something similar