All of these feelings/thoughts can be weird and confusing but they are normal. In the 20 months I saw my T, I had one sexual dream about him BUT it was after a pretty sexually charged session so it didn't stand out to me... BUT since he has left my life, there has probably been about 15 so far... in like 6 weeks.
I only ever saw him as a friend and I truly think that's all I do want because I've never wanted a relationship but no idea whats going on with me, especially with him out of my life.
Everyone will tell you to talk to them about it but I would advise caution there. Most T's expect this but not all are comfortable with it, countless posts on here about people saying similar things and it backfires.
I'd say, if you can, hold off, see if another happens, maybe it wont? Then it's something you can just by pass. You also could get different feelings in the future but it might not be him directly, maybe he represents something or someone else you want in your life?
Happens to most all of us at some point