I think im depressed....kinda rant

I have a 6 week old and since he got here I do everything. I do all the ba y and house care ( I teach so im home for the summer) and my significant other does all the going out and socializing, often alone while I'm at home with baby. I'm so stressed that I bought a pack of cigarettes and have a couple on occasion when I feel so overwhelmed I just don't feel like I can cope. And recently he found out and has begun to ridicule and threaten to take the baby if I don't stop because I'm poisoning him. meanwhile it's ok for him to smoke hookah (tobacco steeped in molasses) around the baby as well. He even got his family in on the ridicule as they decided they could go through my purse and take them like they were doing the right thing. I breastfeed and pump beforehand so that when he is fed next the nicotine isnt present. We are supposed to be getting arrived soon and I just don't think I can do it because of how he openly degrades me in front of others now. I love my baby and want the best for him but I'm so stressed and feel alone I dont know what to do