That sounds like my first relationship (now #2 is hell!!) my first husband and I were married for 5 mos. Before separating. We, also could not get along, but he is a wonderful person!! Our son was 10 mos. Old when I left him, he is now almost 3. At first it was really hard, living on my own, and taking care of him by myself (all by myself, no family anywhere near here). However, my son always has the opporitunity to call his daddy anytime he wants and vice-versa. My ex and I follow the standard custody order, every other weekend, every other holiday etc. He pays child support every month, and he and I get a long wonderfully now!! He is fixing to get remarried, and my son now has two families and he loves it!!!
There for a while he would ask, " where's my daddy?" and I would honestly explain to him where he was. That is the 1st most important thing, always be honest and tell them the whole truth, but do not speak badly of their father in front of them or to them. Do not speak badly of your previous relationship and do not try to win them over. A child's love is naturally divided, and trying to change that will make them end up hating you.
Be strong and just be a mommy, someday someone special will come into your life, and everything will change. Just make sure it's the right person, unlike me. I found someone shortly after the divorce and thought that he was wonderful, we conceived and have since had a child together and now i'm miserable and i've introduced my 1st son to a whole new family and now that's going to diminish as well.
Remember: 1st priority is to be a mommy, do whats best for your child. Everything else will fall naturally into place.