I was addicted to COD4 in the similar way and I realised this aswell. I wasn't feeling happy after playing and yet I always wanted to play more. Hence I stopped playing anything competitive like that years ago. The online gaming scene became too toxic for me to derive fun out of it.I was making 200 kills in CS in the morning and 200 in the evening. I was pure addict of the games of that time.
One day I had a realization. I don't have memories of playing games. I mean I knew I was playing games but my brain didn't think to keep nitty gritty details in the memory. That part of the time is completely blank in my brain. Watching movies, listening to music, books, hiking, going out with friends, travelling etc all these things create memories and emotions that your brain remembers. Gaming is sorta like jerking off, it doesn't create any memories of the process. I felt like I wasted my years playing games. And it's not like games are getting boring they are getting rather good. I'm not against entertainment and I choose to get it by other means.
Anyway, that's my personal opinion about my own gaming.
Now I mostly play couch co-ops and single player heavily story driven games on easiest difficulty.
Really liked Tomb Raider 2013, looking forward to play the other recent Tomb Raiders.