Have you ever fallen out of love while still in a relationship?

To preface this, I haven't found someone new. I just don't know if I'm in love with my partner anymore. We've been together over two years and we live together. I feel like we went from being best friends to "married" so quickly and I just want to go back in time and slow it down because I feel like we're just crashing and burning now. We've been fighting a lot lately to the point where it just doesn't seem worth all the stresss. Even sex has been stressful/non-existent. I don't know if we both changed or what (we're in our mid-late 20s). We are also each other's first real love (we were late bloomers lol) so I don't know if everything was clouded by that and we just aren't compatible. Anyone else ever go through this?