Don't know what his reason for termination was and whether that reason affects this possibility -

What about a posture of: "You did me a favor when you terminated me last year because it...... and now I am so much more stable. I wish you could see how much better I'm doing. I do have a lingering issue with being suddenly terminated, and I think it would help me if I could see you again. I don't know whether you would consider taking me back as a patient, but it would help me a lot to get some closure about it."

Some version along that lines may help you get what you want.