What Could Tender Penis During Sex Suggest?

Why does my husbands penis go soft DURING sex.he is not circumsized, he is 37 yes I am 33yrs. He does hve diabetes but he does not take meds for it . Is it me, is it because he does not feel anything. We have anal sex also and it does the same thing. He used to be fine but here latley this happens and I have to give him oral or a hand job. Pls help me!!!!!