I dunno how I'd feel about having a boyfriend that was into horses.
On the one hand it would be nice having someone that understands the obsession and desire to be at the top, but at the same time unless we had similar training methodologies, etc. I could see it as being just one more thing to argue about.
I love that my boyfriend doesn't know squat about horses. In fact we're both incredibly different people, but that makes everything so much more fun! I love it when he gets me to play some of his online games with him and he enjoys coming out to the barn occasionally with me and learning. I've even given him a few riding lessons, though he's decided it's not totally his cup of tea. Then again I had him riding english. He seems the type that would enjoy western more, to me.
Anyway, I'd probably just be incredibly picky if I ever wanted a boyfriend that was into horses. And to answer the OP - it really depends on the region you're in as to how many men you'll see riding. As well as the disciplines. I'm originally from South Texas so there are quite a few male riders, but pretty much all of them ride western. In the 13 years I lived and rode there I met maybe 3 or 4 male english riders, and saw MAYBE a few more than that at shows. It's the same in Colorado, where I'm at now. However in a few weeks I'll be moving to the east coast (Maryland for 9 months of the year, South Carolina for the other 3 months) and I know there will be a much higher concentration of male english riders, mostly because when I traveled for my interview over there I had a cross country schooling with 2 of them, lol. Our group was actually half male and half female.
"Always be yourself. Unless you can be a unicorn. Then, always be a unicorn."