Dear Single Mother: I'm really sorry to hear that. When my children were 2 & 3, their dad and I divorced. Their dad lived in the same town and didn't see them very much. When they asked why daddy didn't come and see them, I let them know that he loved them, but he worked a lot.
I had a male friend (just friends) help me out a lot with the children, he would go to "Dad" things with them and let them know that he was there for them as a friend. As time went on, they didn't ask about why their dad wasn't around very often as I made sure that there was a male figure for them. I got married again when they were 8 & 9 and the male friend that helped me with my children was my "Bridesmaid" at my wedding. To this day, my children are 21 & 23, they love this friend like an uncle. My husband now of 12 years is a great step dad. They love their dad, but do not respect him or go to him for any kind of advise. They go to my husband or my male friend of many years if they need help from a male figure.
I don't know if this will help, but I sure know that it is hard for you and your 3 year old.