Babies need a healthy mom. Not treating your depression will hurt the baby, especially as he grows and gets more independent and starts pushing your buttons at times.
Weaning him to take meds is a lose/lose situation; there are demonstrated negative physical effects to not getting breastmilk, and it could make your depression worse (you lose out on those great breastfeeding hormones, you may "feel like a failure" etc.)
There are only theoretical risks to the baby from getting trace amounts of zoloft in breastmilk.
Ideally, you'd be able to treat depression naturally through the right foods, exercise, and vitamin/mineral supplements- but we don't live in an ideal world. It takes time and energy to figure out the natural things that can treat depression, and it's really hard to do that while depressed.
I suggest taking the meds to break the depression cycle and keep yourself healthy to properly take care of your baby. Once you're feeling better and your moods have stablized, you can start researching alternative treatments. The long term goal is to get off the meds while remaining stable- but if you need the meds to get to that point, go ahead and take them!