My Boyfriend Breaks Out After Intercourse. They Are Like Lesions,

My boyfriend breaks out after intercourse. They are like lesions, that are red and itchy and then look like a blister in appearance, they eventually do ulcerate or break open, seeping fluid from the sore...it takes a good 10 days to clear up. We have both had the full gamut of testing and all negative on STDs...I don't break out, just him. My Gyn says I am fine and he should see his specialist because he has Crohn's and can be very prone to skin conditions. could he also be allergic to KY Jelly....he started breaking out within hours of us using it. Any Suggestions?