How can I support my partner (35M) who is weaning off after 10+ year usage

I am looking for some advice from people who have weaned off or also supported someone who has weaned off their anti-depressant dosage.

I want to support my partner as best I can but as I have never had any experience with what aide effects he will go through, I am looking for a starting point and advice as the support person, not the one going through it.

We were not together when he started so I am mot aware of any side effects he had started, so am unsure what to expect as he comes off.