I've definitely felt that way. When I lost my first therapist in high school, I was grief-stricken for a long time. I think what finally happened for me was that I just let myself cry and be miserable as long as I needed and I held onto the warm memories of her like... a little light in my soul that eventually stopped flickering and stabilized. I subconsciously finished internalizing her after a while. She did give me a tiny little teddy bear and that helped. I also had a song that reminded me of her- I listened to it a long time... music helps me process my emotions, I wonder what might help with yours.

Also, is there any reason you can't contact him?

I don't think there's anything wrong with touching base for a one time session or to ask if he'd write you a note to help you hold onto his presence better or something.

My therapist moved to China, so, we couldn't keep in contact (this was before email was well established and everyone had computers), but if you are able to, I'd jump at the chance.