I wouldn't suggest trying anything sexually with a guy you (could) have deeper feelings for. Especially if your husband thinks it's all about sex. He deserves to know what's going on going into a situation and what is going on is that you think you could have some real feelings for this friend.
My husband and I started out swinging and discovered poly sort of by accident. Our swinging life had definitely taken a more "exclusive" form than most swingers (we had one couple we played with and we were the only ones they played with as well), and eventually she and I realized our friendship had morphed into something more. We both kept our husband's informed at all times.
Personally, I think the line between cheating, swinging, and poly can become a bit blurred. When you're swinging, you have permission to have sex with others, but if you develop feelings and act upon them it is most often considered cheating. With poly, you can have sex AND an emotional relationship, and generally the only way you cheat is to lie about something or to break a boundary you had previously set up with your partner(s).
So, I would worry that if you act upon ANYTHING (crush related or sexually) with this friend, and THEN tell your hubby that you have these feelings, he could quite possibly view it as cheating. Because you weren't fully up-front and it wasn't just about the sex.
If you're all close, and you think there may be other sparks flying (between hubby and friend's gf, friend and you, or any other combination besides just you towards friend) then talking about it wouldn't be a bad idea. But you definitely don't want to muck up a perfectly good friendship/roommate situation by admitting you have more than friendly feelings towards someone who wouldn't even consider the idea!
I would recommend talking to your hubby. Tell him everything. Get his advice. If he's the guy's best friend, he will have a strong opinion about it, I'm sure. Who knows if it's positive or negative until you ask?
One thing I've noticed around here is the differing definition of "crush," too. What do you consider a crush? I consider a crush being the beginnings of romantic feelings so that's what I've interpreted it as. lol Please let me know if you think of it as something different!