Hi Belcano,
When you talk to your counselor about this, I would definitely mention that you're not certain what kind of boundaries you're even supposed to start with. As Heather said, you're in the driver's seat when it comes to if or how you reach out to your ex. But if the goal of that exercise is to help you with boundaries, it doesn't make a ton of sense (or feel entirely safe) to reach out to your ex prior to getting in some solid practice setting boundaries elsewhere.
I'd also encourage you to share those feelings of this being a big, life altering thing with your therapist. One thing they might be able to help you with is to re-frame the situation a bit. When we frame a choice or a change as this giant, life altering thing that will change everything forever, it can often up our anxiety.
It sucks that you're feeling alone right now. Have you had any luck keeping up positive social connections during social distancing?