Hi Marzi..
What a difficult position to be in
Addiction including recovery can be a very personal journey, do you think your dad would have minded his “sponsor” telling you , just feels a bit off this coming from his trusted sponsor and not himself doesn’t it..
Perhaps just reach out without letting him know that you know that peice of info (ask yourself who benefits from letting him know thst you know ..). Take things slow, see if he opens up , gauge where his head is at… Then maybe start to ask the more difficult questions.
Wishing you all the best xx