You can confess to him, but you can also further your agenda without confessing. Just do with him what couples do together. If he goes along this will give more time for both of you to adjust to the possibility of a relationship.
So invite him to do stuff involving just the two of you (the specifics depend on your common tastes, but probably going to the movies, or to the park, or to each other's place. Also don't hesitate to touch him, this creates more intimacy. In this whay you can build a de facto relationship without forcing him to decide quickly upon being confessed to.
If this works out and you are all but in name dating, then confess to him. But this is only one way of getting there. Perhaps the direct confession could also work, considering that you are doing so well together.