There are a few things here to be cautious about but you need to find out what you want and how you feel. You obvisouly care about this guy becasue you were so upset with him for not knowing what he wanted ealier in the relationship.
One thing to be cautious of is how fast things are moving along. He has already said he wants to be cautious because of his Ex-marriage so this could be a red flag. Because of him still dealing with his Ex and not to hurt you, but you could be a rebound relationship so to speak. One to aid him and help him get out of his bad marriage.
On another note, being a step parent is a big responsibilty. And obvisouly kids are involved and probably see him frequently, and while the child is old enough to understand things. He needs to let the relationship go with the flow for awhile before just moving you in and so on... Nothing against you at all. I just think when kids are involved, parents need to be relaxed when it comes to their relationships and jump into something right away.
If you can't handle the thorns, don't crave the rose!!