How do I break up with someone I've living with?

I’ve been together with my gf for a year and 5 months. We’ve gone on to move in together and have only lived together for a month. But already I know it was a mistake to do so. I feel like I’m letting her and her family down (all graciously helped us move in). I love them all but the romance isn’t there anymore for me. I feel terrible since I think I should have recognized it earlier.