Long story short, me (25M) and my 5 years LTR (24F) are planning to move together, we are buying an apartment for ourselves. Im having serious second thoughts, sex is by no means great, shes great (have really good morals, i was her first man, strong family values) she recently gained weight (20lbs) and sexually I'm losing interest. I don't want to break her heart if i say I'm no ready for moving to the next step because it would mean to break up. But also i have this urge to talk to every nice chic i ran into (several have flirted with me but i blew them off). Please help!! What have you done in this cases?

Edit 27.03:

Thanks a lot for your responses. I cleared my mind, had some days off of everything and realized what I already knew, that i have to be true to myself and man the hell up with my live. The truth is that i wasn't afraid to take the commitment, i do not buy by the idea that "she's the one", but i do think that she is wife material. I talked to her once i set my mental house in order with What i wanted for my life. That was a relief for me and her, i could see. I realized as another member here told, that she was following my beta behaviors. I told her about my discomfort with her laziness and she started working out every single day since i told her. I also start working out twice a day, restart learning to play the guitar and finish to read a book i left unfinished.

Thank you all!