What I am gonna say, comes from a place of experience and understanding (I have anxiety to) but also concern.

From my own experience, I would like to suggest as best as possible to try not to think of "What if" with Therapy. The fact is, NO ONE knows how anything will end. Therapy WILL end at some point, but so will every other relationship in life.

I spent so much time early on with T freaking out about the ending and it caused me to miss out on so much of the moments we were having. I wish I could have had more moments to remember, and enjoy. I wish I hadn't spent so much time in my head, fearing what I knew would happen eventually.

Ideally therapy WILL end on the clients terms, but not always. That doesn't mean you can't enjoy it for today. You are still his client today, you still have him. Try to remind yourself of that simple gift.

I don't think any normal therapist will terminate a client because of attachment, unless the client becomes like a stalker. Wishing all the best for you