Sucking his fingers after he fingers me?

Okay so the guy I'm messing around with always puts his fingers near my mouth and in my mouth after he fingers me and rubs my clit.  He wants me to suck them, and I do cause I know he finds it really hot.  What is your guys opinion on this?  Do any other guys do this to you?  Is it gross?  Would you suck his fingers and he fingers you?