I completely understand how scary and confusing this can all be, and I'm sorry to hear that things escalated to that point.
First and foremost: obsessing over suicidal thoughts or just "feeling suicidal" is one thing, and can be addressed through the techniques discussed here with or without a therapist. If you honestly made a physical attempt at your life, however, then I plead that you find a professional to talk to as soon as possible, and preferably face-to-face. You can only get so far reading text written by strangers, especially strangers that don't know you or your whole story.
With all of that in mind, I'm happy to give my advice based on what you wrote.
Alcohol really inhibits our ability to truly be aware of what is happening in the present moment. This makes advice like being mindful, allowing the thoughts to be, and sitting with the feelings, somewhat futile because they completely rely on our ability to be aware. I'm not here to tell you to stop drinking, but I would very carefully consider your mental state before going out for a night where you might get drunk.
When you are out with friends or your girlfriend, I would say the only thing you really have to do is expect that intrusive thoughts will arise, and to simply notice when they do. No matter how terrible or frequent they are, the only thing you have to do is recognize them as intrusive thoughts. You can think, "ah, there's that violent thought again," or, "I see you, violent thought. I will come back to you later when I get the chance." They might stick around the whole time you're out, but they don't have to be in the foreground of your attention. Focus on what is right in front of you, regardless of the chatter in your head.
The goal is to have the mindset of, "I'm enjoying a night out with my girlfriend AND I'm experiencing intrusive thoughts," and understanding that things can happen at the same time.
It's not the content or the frequency of the thoughts that causes any problems, it's when you grab onto them and get taken for a ride that you really suffer.
This stuff takes practice, and will gradually get better over time with baby steps.