how to quit without a "why"?

currently, i'm in a substance use partial hospitalization program at the request of my psychiatrist. I've quit before and was sober for a year until my girlfriend of 4 years broke up with me. i wanted to be better for her and make her happy and proud instead of disappoint and upset her. now that she's been gone for a year and a half, I've been drinking the whole time because there is no "why" anymore, and i can't think of a worse "why" than myself. when i was sober, i didn't feel any clearer or more connected. i was less charismatic, more sorrowful, worse at my job, and had more brain fog. i don't like my parents or family enough or have any close friends that I'd want to get sober for. i practice hobbies like painting and drawing, film and tv, exercise and weightlifting, video games, but i don't actually feel connected to any of them, definitely not enough for them to be a motivating factor of sobriety. now that i'm in program, i see a psychiatrist twice a week, but I've been cycling through medications for 11 years now, so they are as unsure of what to do next as i am. it's kind of a stuck loop where they tell me that maybe the new medications won't work if I'm drinking, but i was on so many medication trials during my sober year without any positive progress that I'm just not willing to be sober indefinitely with 0 personal desire to do so or any plan that might give me the desire to do so. i can't get sober as a revenge "look at me now" sort of thing to my ex because i know she's moved on already and isn't coming back, so that doesn't motivate me either. i know this is difficult and probably doesn't have any clear answer, but any advice is appreciated.