I don't sugar-coat either. Ds first asked about where is daddy, when he was two - I was not expecting it at all and said 'he ran away'. Which he did.
Not sure that was the best thing to say. A couple of years later he asked if daddy ran away very fast 'like this..' then he ran across the room really fast. Lol. I explained a bit more - no, he drove my car up to London and caught a plane and didn't come back.
I explain now (he's 6) that daddy was a silly man and didn't want to be a dad as he wanted to do other things, but that when he left he DID know that I would do a very good job of being his mummy and that he knew I could love ds enough for both of us (me and x i mean)
Ds and I often have chats. We snuggle under a blanket and talk about things. He says he thinks about his dad quite a lot. I say that's fine and it's not surprising, and if he has anything to ask me, then he can and I will tell him.
He doesn't have a very high opinion of his father though does want to see some good in him - eg, when I repeated the other day that Xh knew I would look after ds very well on my own and love him enough for us both, ds said 'well that was quite kind of him really'
It's very hard. Ds would love to have a dad. It's hard as we live in a tiny rural place and most of his mates have married parents who are together.
I also remind him that families are all different - some little boys have a dad but no mum, other have a dad and mum who don't live together, others have no mum or dad (orphans in africa etc)
I have made a big 'Dad Box' to show him when he's old enough. Containing love letters, photos, pictures of Xh holding him as a baby etc.
I don't know where his dad is now. He pays nothing, never has. I hope he never returns and have to say I would be upset and concerned if ds wanted to find him one day. But I wouldn't stop him. I would help, but he would have to know the full truth about his father if he did.