I'm loosing my Halo interest... i really don't kow.

I think  i hit a wall or lost my mojo for halo. I purchased Reach on release day and played for a couple of hours and have not touched it since.  I have just no desire to continue, i liked what i played so far so that's not the problem. I just purchased the Onslaught  pack for Bad Company 2 and I'm playing it as soon as i finish writting this. Again i ask myself when will i play Reach again?