hi selma and welcome!
i would render a bet that if you dug around in his past, you might uncover a lot more problems that alcohol caused in his life than the one seizure.
i think it's a red flag that he downplayed his drinking problem and abstinence as a new year's resolution.
i think it's a red flag that he said it was under control and then started drinking again.
i think it's a red flag that he is not seeking any help with his drinking.
i think it's a red flag that he is around drinking as his job.
i think it's a red flag that he started drinking everyday and you noticed a change in him.
i think it's a red flag that you feel it's a bigger problem than he's admitting.
let's ignore what he is saying for a minute, and look at what has actually HAPPENED:
since you asked what you can expect in the future, i would render a guess that you could expect much more of the same as has already occurred. as in he gets some sober time under his belt, thinks he has it under control and then starts drinking again. when he starts drinking again, he will change as he did before.
if i was you, i would get to the bottom of this and determine how big a problem drink really is. here are some things for you to look for:
1. does he have a valid driving license?
2. is he always borrowing money from you?
3. what happened in his previous relationship? why did they split?
4. does he get angry when you bring up his drinking?
5. have there been periods of time when you haven't heard from him for days?