I'm attracted to my so's older brother
What is the reason why you are so attracted to him? Is he a lot older?
He is just super romantic and he has a great sense of humor.
It is a bad idea to get romantic ideas about your so's siblngs, this can only lead to lots of hurt feelings. He sounds like he is too old for you anyway. You should either focus on your relationship with your so or break up with them.
You are mean. I'm leaving.
It is just a much better idea to focus on your partner than their older brother. If you feel attracted to their older brother much more than your partner, then this could be a sign that you maybe should not be in that relationship any longer.