Why would a drop dead gorgeous,talented,smart charming and incredibly funny guy feel threatened by a gay man?

I've been with my boyfriend Jackson for about 6 months now and he's pretty much as close to perfect as one can get but for one thing; he has a real problem with my relationship with my gay best friend Justin.Justin and I have been best friends since we were 13 and we're all 21 now.Justin and I are as close as two people can possibly be and I'd go to hell and back for him as he has for me many,many times before.Justin and I talk on the phone several times a day and regularly go to the movies,shop,meet for lunch or coffee,cuddle on the sofa watching dvds and sleep in the same bed in each others rooms when we stay really late at each others places and don't want to drive home tired.Yesterday morning my boyfriend found Justin and I in my bed ,him in boxer shorts and me in a pj tank top and short shorts spooning and flipped out.What exactly is his problem?Justin is gay after all.