You need to contact Alanon it's for the families of alcoholics, you'll get support there.
There's plenty of help for your partner to quit alcohol and drugs but he has to want to do it. And for himself. He can't do it for you or anyone else. He needs to do it as both will make his depression worse in the long run, even if he's using them to self-medicate in the short term.
It's not as if there's no medication out there, it's just not stuff that will knock you out or give you a pleasant buzz. There's basically no excuses for self-medicating. It's self sabotaging behaviour. Nobody can recover when they're sabotaging their own recovery. It's the first thing that has to stop.
There's nothing you can say or do to make him want to get help. Except perhaps leaving. Lots won't get help until they reach rock bottom. While the illusion of normality is still there (partner, job, money for bills etc) they can tell themselves they're fine, coping, not out of control.
Whether you stay or go, your focus has to be on maintaining your own mental well-being. There's lots of advice online for this. Basically sleep well and enough, eat healthily, no excessive drinking, see friends, create a calming home environment (which you may eventually realise means not living with an addict), take time for relaxation daily.
Don't let your partner take over all your time and energy. It's not your job to "save" them. Nobody can save them except themselves. Have very strong boundaries and use them to protect the time you need for maintaining your own well-being, whether that's an exercise class, a meal with friends or cleaning the house. You're entitled to look after yourself and you don't have to be available 24/7 to deal with a crisis. It's ok to switch off your phone.
Look up coercive control and other symptoms of an abusive relationship, because the nature of addiction means abuse goes hand in hand with it. Contact Women's Aid to get support in that area if necessary and consider doing the Freedom Program.
Regarding depression, you can get the police to do a welfare check if you're concerned about your partner harming himself (and he's not with you). Your partner can go to A&E to be assessed by the duty psychiatrist any time if he feels he can't keep himself safe ie alive and unharmed. He may end up with a long wait for that assessment, put on a psychiatric ward for a while or may be discharged after being seen. If his GP isn't aware then you can tell them about the addiction and MH problems, although they can't respond to you for confidentiality reasons they can listen/read what you have to say and request your partner make an appointment. If he chooses not to see the GP or take their advice, nobody can make him.
If there's any bad behaviour don't cover it up. People often don't get any real help for MH unless life has fallen apart to the extent they are a danger to themselves or others. Call the police if a crime is committed, including domestic abuse. It will help him get help. Don't hide what's happening from your friends, you need their support now.
Sorry that's so long. It's hard to know what advice you needed. I hope some of it helps you.