Oh man I know exactly what you're talking about. .. I am currently in a similar situation and do not know what to do either. Wish I could tell you how it worked out, but it's still ongoing so I don't know yet either and that's the scariest part: knowing that I could just continue with my gf forever without having any real fights or problems and get married but always feel like my gf is just a friend that I live with. It's hard to shake out how much of my current dissatisfaction with the relationship is due to me being stressed, busy, and tired all the time and how much is actually my feelings for my gf waning or changing. It's so easy to just continue in a relationship like that, especially when you share friends, know and love each other's family, and become totally entwined in each other's life.

I guess my question to you would be have you ever met a different girl who you thought you would be happier with? A girl in my class that I am close to gives me those feelings that I used to have with my current gf, and for that reason I think I may be ending things sometime soon. It's just so hard to give up comfort for the unknown. Really do some soul searching and try to figure out if you do still love her or just carry a fondness of her like you would have for any friend that you have been so close to for so long. Breaking up would be seriously tough but it might not be best for you to continue and get married and have kids now just because it's the time when you're supposed to or because it would be practical. I personally don't know if there's a way to get that feeling back once it's gone,but I do know that your first obligation should be to yourself and your own lifelong happiness, not to a time line that you feel pressured to follow.

I guess in the end I don't really know how to help because I am currently in a very similar situation and dealing with it by doing nothing. All I can say is that I sympathize with you and you're not the only one who is experiencing this feeling in an otherwise great relationship. Good luck to you and I hope you are able to talk about the issue with her and figure things out. At this point, she may feel the same but feel like she doesn't have enough time to find someone else and stay on her schedule for marriage/kids. If she is feeling similarly to you, I think it might be best to try your best to move on gracefully and find someone who gives you that feeling again. I dk I need to stop talking because this isn't going anywhere. I sincerely wish you the best of luck though man.