Am I in the closet??

I know that's such a dumb title, but that's pretty much how I feel right now. I'll start out by saying that I'm currently in a long term relationship with a girl, who I really do love. We have a pretty healthy sex life and her vagina doesn't gross me out or anything, BUT... there's a whole other side of me that nobody really knows about. Since I've been about 12 or 13 (25 now), I've checked out all types of porn, but I would say that at least 80-90% is either gay or transsexual (and if it's transsexual, it's only if the guy involved is a bottom). I've also hooked up with a guy before, and we've sort of been texting back and forth for the past few months. He's been really helpful and has done everything short of telling me to come out haha. I know I'm rambling, but this is pretty much the first time I've been open about these feelings. I think of dick all day, and as soon as I get home, I look up porn and imagine myself pleasuring another man. I've really considered ending the relationship, but I don't want to break her heart. But it's getting to the point where I'm really feeling the urge to be with a man. I also feel that I don't want to look back on my life when I'm 80 and say "what if". If someone who's been in my situation before has an opinion, I'd greatly appreciate hearing it. Any suggestions on what to do? Sorry if this is a dumb post :(