My boyfriends Penis problems...?

I know i had a similer question to this but now its starting to annoy me. Befor i understoof why.. I supprised him but now when me and my boyfriend have sex AND HE KNOWS WE PROBABLY WILL IF HE HAS A CONDOM AND THINGS LEAD INTO IT. He still dosnt get hard. He gets hard when were makiing out and crap but RGHT when i put tr condom on. BOOM he goes frikken soft. He keeps sayings hes overly happy ? But it makes me mad.. No mean comments. I just want to no why he cant stay hard.