All advice welcome, please!!!

I'm embarrassed to talk about this so freely but I need some opinions on this topic. I'm 22 and my SO is 29. My SO and I are very sexually active, active to the point that there's maybe 3days besides during AF that we don't have sex. I try to keep it exciting by trying everything under the sun including every position I can think of and different places as well. Well here in the past couple of weeks I've noticed that after he gets me off he stops (not finishing in me like he normally does) and proceeds to masterbate. I almost always offer or put up some kind of assistance to help him during. But he's doing it so offen now that I don't want to put up that assistance because it's upsetting me that he's doing it so much.