Does he love me or is he afraid to be alone?

I have been in a happy relationship for almost a year and a half now, M is 24 and we have been talking about moving in together next summer. I was head over heals, and I still am. The problem is that lately I have the gut feeling that I love him more than he loves me, and the feeling of having so much unanswered love hurts like hell. I was ripped of my cloud nine when he suddenly told me that he had been feeling down lately and that his feelings of passion for me are fading. This really shook me, I am his first girlfriend and I explained that after awhile, the shine of a new relationship fades but love stays. And that that's a moment when people decide to stay or not. He felt better after that, but I am feeling worse everyday. Sometimes when I smile at him he doesn't smile back, and he doesn't squeeze my hand as often as he used to. I have asked him, and he says of course he still loves me, but I have this nasty feeling that I put more love into us than him. We still sleep together but what if he just does it to please me and not him? What if he's just afraid to be alone? I really want it to work but I don't want to beg someone to stay or sugarcoat everything that I do because I'm afraid that he will leave. What do I do?