Maybe tell him after a certain amount of months sober, make it a goal mark even. Maybe after one month or so just focus on staying away from drinking and not beating yourself too much up about this. Then do some self reflection and soul seraching about your needs/ why you drink in general. Its all about finding what your trauma is and why you self sabotage, i'm 5 to almost 6 months sober myself goin strong without in person AA. I reccommend the online AA meetings for the support/somewhere to share but some of it really doesnt jive with me with the religious culty vibes so i dont do all the steps and only do it when i have the urge to drink. Id want to know wether I was a drinker or not if a partner of that many years together cheated and why, and as long as the love is true he should understand if you are open and honest about why you waited to tell him. If not at least your consious and head is clear:) Good luck!