Trouble with a teen? No, really?

I'm having trouble with my fourteen-year-old.  I'm sure you're shocked.

Up until recently we've had all the best parts of the mother-son bond, plus the usual good behaviour and eager-to-please traits of the oldest child.  But lately, he's sullen and quiet, speaks in grunts (if at all), hides behind a wall of greasy hair, grumbles about doing his chores, and complains endlessly about going to school and his teachers.  I never see him reading a book anymore.  What really drives me to distraction is his butt, because it's constantly parked in front of the computer.

But you know what?  He loves, loves, loves our foster baby.  From the day the baby (let's call him Baby B) came at two days old, my son (let's call him Boy A), has been a huge part of B's life.  A. had no warning that B. was coming; A. came in the door from school, hung up his coat, turned around and saw the baby lying on a blanket on the floor.  After standing frozen for a moment, he nonchalantly remarked "We have a new foster child".  Later that night he was stroking the baby's head and said "Mom, this is great, we get to have a cute little baby, and I never have to have an annoying little brother!".  He babysits for me (when I'm working, and I pay him $4/hr for that), but he also "brothers", which is when I say "can you just take this screaming baby for 15 minutes so I can have a shower?", and he never says no.

And you know what else?  He grumbles about his chores, but he does them.  He complains about school, but as far as I know he has never skipped a class yet.  When we go to the library together (which we still do), it's so obvious that the kid's and YA books are too easy for him, and the adult books don't interest him.  When we're at home and nobody can see, he still calls me "Mommy" and gives me big hugs, and kisses me goodnight.  (Sometimes it's me going up to bed first these days.)  And how can he be hogging the computer if I spend so many hours of *my* day in front of that same computer?

I get tied up in knots about perfection.  As a break from worrying about my own shortcomings, I focus on his.  My Mom was the same way, and after internalizing that worry about never being good enough, apparently I'm passing it on.  Why would I do that?  Why wouldn't I love him just the way he is?

So, yes, I'm having trouble with my fourteen-year-old... but I'm starting to think the trouble is really me.