The normal function of the penis is to "spring" back into the body (note that most animals do this even more effectively than we humans) when not in use, and particularly in order to be protected - when you are active.
It does so particularly when you are cold - and it is somewhat more difficult to get an erection when you are cold anyway. Since the only
time the skin is provoked to stretch, is when you actually stretch it, how small the foreskin springs back to afterward makes no difference. In fact, you want
it to be just that elastic.
you haven't had problems and sex is "normal" with a foreskin that does not retract. It's almost "normal" without a foreskin at all - that is, circumcised, so having a non-retracting foreskin is actually somewhat similar. Mind you, if you stretch it up to retract, then you can do things a circumcised fellow never can (and those things are valuable).
I have to observe that if having sex encouraged your foreskin to stretch and retract, you should be perfectly retractile by now, shouldn't you? Well, it does help a little
, but the prolonged stretching is the main focus.
reported that you will notice some irritation from stretching, which just means that something is happening. This may vary from time to tome, sometimes noticeable, sometimes not. It is also
possible that the minor trauma can predispose to "Thrush" (Candida; yeast, which you can exchange with your girlfriend) so it might be worth trying treatment for that if there is substantial irritation.