Hello, If you have unprotected intercourse, the ejaculated semen can give this sort of smell after sometime, especially after mixing with the vaginal secretions. If you have had the vaginoses excluded, your sexual partner may need to get examined for any urinary infections and/or fungal infections, more so since he is a diabetic. If needed, he may be treated. Diabetes per se does not cause any odor, but, if it is uncontrolled, the higher glucose content in the secretions could cause some issue. Hope this helps.