First of all OP, in your heart of hearts, do you see this being a long term relationship? Have you discussed living together, marriage, etc? If not, then wait to introduce them.
If you're BOTH sure that things are headed in the direction of a 'for ever' type relationship, then I would arrange to bump into him somewhere that you take your child on a weekend, and introduce him as Mummy's friend. Stop and chat for a couple of minutes, and then move on. Then arrange another opportunity for a casual meeting, for example if you have a garden, perhaps you could ask him to come and cut the grass for you, tell your child that the friend they met is coming to do some gardening to help you out. Then when he's finished, invite him in for a drink, and give your DC the chance to get to chat to him that way. Or if he's a carpenter, or a plumber or whatever, get him to come and do some odd jobs, so that your DC can get to meet him again that way. Then if that goes OK, you could perhaps arrange to meet up for a picnic one day - again, tell your DC that you saw your friend, and he asked after them and wondered if you'd both like to meet up for a picnic one day, and would they like that? Be very careful at this stage not to be too flirty or playful, or touch him in any way, as kids do pick up on these things really quickly. I think the most important thing, is to do it really slowly, over a period of weeks and months, until you know if he and your DC are going to get along. However, be VERY watchful for any warning signs that he's over bearing, or complains about your child afterwards, even if only a small thing, it could be a sign that he's not going to be good SD material.
Above ALL though, please be sure to put your child first, as NO man should ever be more important than our kids.