You're on the right track when you're apprehensive about it, for the right reasons
If the first one is exhausting, now you'll have to divide your time even more. Keeping them together during the day would be a recipe for disaster and destruction. Getting a second dog as a playmate is never a good idea...especially if you don't REALLY want another dog for you. You'll end up with TWO dogs you resent.
Focus on your boy- this is a tough age (teenagers!). Are there any classes you could take? Do you have any interest in agility, etc? What kind of training do you do with him?