Am I a lesbian?

Sometimes I feel like a lesbian with a boyfriend.
I like my bf (we've been together for several years) and like having sex with him....but I'm not attracted to other guys, have fantasies about dudes, or have ever enjoyed imtimacy with another guy.
Any other penis is scary! So scary that if I broke up with him I don't think I could be with another guy.
Sometimes I wish he was a girl, which sounds really strange.
I told him how I felt and he became really angry and said "if you like girls and you're with a guy you're bi"
Does any one else feel this way?
Am I a lesbian?