I've been dating my gf for about 17 months now. We've had plenty of ups and downs and I love the girl, but I still have plenty of doubts about us in the long term. I was out the other night and saw a girl that I had a crush on 10 years ago. Havent seen her since.
We were talking and having a great time at the bar. We just clicked and she's single. We have so much in common, even more than me and my gf, and I feel like this girl is a better fit for me.
Its just such a difficult thought process on what I should do at the moment. Does anyone have any advice?

Do you know this other girl really well?

Don't give up everything for a girl that SEEMS just so perfect.

The grass is NOT always greener on the other side..

We used to hang out in high school, but I feel like if I dont express my feelings to her, its going to eat away at me. I really dont know how to handle this situation.

"hanging out" is not equal to knowing this girl really well...

Do some stuff with her, just as friends, and look what it gives.. But you should state her you have a girlfriend from the beginning. If after quite a period you really feel SO much better with her than with your current GF, start to consider.

This is what I wanted to do, but how do stuff with her as a friend when I have a gf? How do I even ask her to consider this?