Here is what I think about people who cheat...
If you or your partner, significant other, wife, or husband, or whatever you want to call them, even thinks/fantasizes about wanting to be with someone in any way, then they have a problem. That person is then not committed
to their partner, etc. When it gets to that point, they need to go to their partner and there should be some discussion.They should not have even waited for it to get to that point.
Quite possible they need counseling. There is something wrong with their "heart". You should only want, think about and fantasize about your partner, etc.