Guys - is it ok to have a crush on someone while in a relationship?

well i can't say that i would think its right to be having a crush on some one else while your in a different relationship that sends the wrong message why if your in a relationship with someone else why would you be having a crush with someone else it just says that if you ever could get with your crush you would leave the relationship your in to go to the other and ask yourself would it be far