Okay you've been with your current GF for 11 years?
You're pretty much married. Long term relationships are HARD they require work. And if you expect them to always be effortlessly easy and happy then you're in for a real surprise. It's also not uncommon to long for other people, even when you love the person you're with.
This is normal and it doesn't mean you have to jump ship. In fact I would suspect that your "crush" will fizzle if you leave your GF because it's really just a manifestation of the 'plant my wild oats' part of your brain wanting to be free of the shackles of monogamy.
So... in short if you want to make your relationship work (and you have to want to to make any relationship work) you can. You just have to put some umf into it.
If you don't. Go and jump ship. But realize that you're going to be in the same boat again eventually and you have to, at some point, decide to work hard at a relationship or you'll for ever be thinking the grass is greener else where.
I direct you to Dan Savage who can explain what I think you're going through right now.