There's nothing wrong with uncertainty in relationships of any type, including friendships. It's common, especially in the early stages, when you are developing something new. I think it's smart that you want to listen to your therapist. Trauma and mental illness are no joke and they can have a huge impact on relationships and how we feel about them. I think it's good that you're cautious and wanting to work on yourself.

However, I also believe in creating vulnerability and asking for what you want. What you said above is quite elegant and open, and I don't see why you can't approach him with it like you told us. I know vulnerability is scary, especially if you're the one to go first, but it shows an example of openness that could impact your relationship in a good way, whatever that may be. You can tell him you aren't sure how you feel. You don't have to have everything figured out before you approach someone you care about. Maybe he can even become some of your support team as you heal and grow.

Good luck and PM me if you need anything.