Boring sex

I've been married for 3 1/2 years and our sex life sucks. We have sex every day BUT it's so boring. He doesn't explore anymore, he never wants to have "kinky fun" and he has just gotten to a routine, and it's made me want to sleep with his friend, his Friend is attractive & fun and hot af and thinks the same about me, my husband wanted a 3some with this guy, and I so desperately do but then my husband said he'd divorce me if I wanted a 3some. So I'm fucked. What would you do?