I'm with Tarpon in that it sounds like a psychological issue on his part, especially as you say this has been ongoing since you've been together, rather than a sudden change.
It is easy for anyone, man or woman, to become used to a certain way that works. Some women can only climax with the use of a vibrator, for example, and sometimes in that case a kind of retraining can help.
I know my husband says things like not enough friction sometimes. Generally, if I'm too wet (apologies if tmi) he'll just enter from behind as that makes it easier for us.
Seriously though, if you are worried that you might be loose, go see your ob/gyn. They can rule out any possible medical explanations, but I'm sure you're fine!