Oh man, I totally have the answer to this, it was on Embarrassing Bodies! If it's Retrograde Ejaculation, you'll be able to tell by his urine, it'll look a bit stringy. Basically the prostate isn't filtering properly and his ejaculate is going into his bladder instead of his penis. They said 35% of men with diabetes have this problem, and it's easily fixed. When I'm not on iPhone I'll PM you the link