My significant other's friend is married but I can't help having a crush on them.
Whoa. Do you think this could be something serious or not?
Maybe, I'm just wishing that she could leave her husband
This sounds like a terrible idea.  You should remain loyal to your SO and your SO's friend should definitely remain loyal to her husband!  Cheating is just straight up bad!
I would never be disrespectful to her husband like that by stealing his wife.
Good, because you have someone already and so does she. It would be considered creepy, wrong, and not to mention gross if you ever tried to act out on these feelings.