I’m attracted to my old foster cousin

So first off I don’t want any negativity.

Here’s the story, my aunt fostered this guy 15ish years ago. She only fostered him for maybe a yr or 2. She never adopted so he is not really my cousin. We have remained friends through the years because we are the same age. Recently we had lunch together and there was definitely an attraction for me. Let’s just say he glowed up for sure. He also made a comment a few days ago saying he thinks I’m super sexy with red hair (I dye my hair) I have never thought of doing anything with him because I didn’t know if it would be weird, now a few hours ago he asked to be FWB , so my question is, would it be wrong if we did anything together?

Mind you we are not blood related, no same family, he just lived with my aunt for a year or so.

Again please no mean/rude/negativity