Sad and disappointed

I can't seem to concentrate or focus, my mind is going 100km an hour and I can't get it to settle on one subject. The only thing I know is that I'm not happy. Not in my relationship or with my life as it is at the moment. What I want to figure out is if I change my habits and lifestyle would that change my feelings about my relationship or just reinforce my current feelings of unease and unhappiness? I have two beautiful boys to think of as well. The oldest is already pretending to smoke cigarettes which just breaks my heart. I'm also not happy with how often they (and myself) are exposed to second hand smoke from my partner and his father. Even though they smoke outside it doesn't stop the smoke from effecting us especially when there isn't any wind to blow it away. They just don't seem to care or understand that it is wrong to be smoking so much around such little babies. Should I just stay alone and depressed so the kids aren't exposed to it so much? If that's the case should I just be single and work on myself to be a better mum for my boys? If I become single and have to share my boys with their father is he going to do the right thing or not by the boys? Or is he just gonna leave them so he can smoke and play games? Too much happening inside my head for me to make a decision and my boys are the ones suffering because of it. I need help and advice but most of all I need courage to do what is right by me and my boys. I just wish the father of my boys cared enough to do the right thing too.