If you're really unmotivated about continuing your guitaring why don't you try learning songs that you like, instead of learning mary had a little lamb crap out of those teaching books. Look up guitar tabs on the net and have a go at songs from a genre of music you enjoy listening to. I wouldn't sell your guitar, just because you're unmotivated at the moment doesn't mean in the future you won't want to pick it up again. There's no reason why you can't have a go at both guitar and drums.