I realized I didn't answer, I will stay with him regardless.
I think this is an important starting point. Knowing that you'll stay with him regardless means that you can avoid making empty threats you're not going to carry out and focus on what you need to do for yourself in order to remain in the relationship without sacrificing your happiness to your SO's addiction. If he knows that you'll stay with him regardless, then you need to make sure he also knows that doesn't mean you'll tolerate unacceptable behaviours.
Because you're worried about how he'll react to you being honest about your own feelings and fears, it might be worthwhile talking to a professional who specialised in drug and alcohol abuse. A professional can also help you with establishing healthy boundaries - choosing to stay with your partner doesn't mean you need to tolerate abusive behaviour from him when he's drunk and a professional can help you learn strategies for minimising the harm your SO's addiction causes you.
It's honestly hard to tell how an addict will respond to "I love you and want to help you". He might feel guilty, he might use it as a hook for co-dependency and cast you in the role of rescuer, he might get hostile and tell you it would be easier for him to quit if you didn't "pressure" him (especially if you say anything along "life would be better" lines).
What you need to understand is that him quitting or not isn't dependent on what you do or say. That you're worried whether it will "help" or "depress him more" makes me think you might not fully understand that yet and that you're willing to suppress perfectly valid emotions when you fear that expressing them might somehow affect whether or not he succeeds in quitting.
It's reasonable for someone who says nasty things to their partner when they're drunk to feel guilty. Are you concerned that if he feels guilty he'll wallow in that guilt and drink to mask the emotional discomfort feeling guilty causing him? You can't reasonably live your life trying to avoid doing and saying things which might make your SO feel emotions which he finds uncomfortable because "it might depress him".
I've been an alcohol abuser and I the only time I ever went near an AA meeting was when I accompanied someone else who was court ordered to attend. There are plenty of other options for anyone serious about quitting drinking and someone who's serious about quitting will actively explore those options.
Your SO may have been able to quit on his own in the past, but he wasn't able to either remain abstinent or establish healthy drinking patterns following that. Even if your SO truly believes he can quit on his own again, both quitting itself and not returning to abusing alcohol will be easier with outside support. If he's saying how hard it is, then I'd approach it on that basis - yeah, he probably CAN do it alone, but why not make it easier for himself and take advantage of outside resources (this doesn't even have to be formal counselling - there are a range of medications designed to help people either remain abstinent or reduce their drinking).
I think that for many people rehab is the best option, but there's no point in half-assing it - and I think it's important for people to understand that relationships don't always survive an addict becoming sober and be prepared for that possibility. The fact that he's had previous addiction issues does make me think that rehab might be the best option here, but I also think that you need some kind of professional support for yourself regardless of whether he decides he wants to quit or not. He's ambivalent about getting help for himself and you can't control that. You can control whether or not you get help for you, though.
