I had a one-night stand and I hate myself. Should I tell my partner?

Well, you have lived through many years of trauma, some of which is caused by your family, as you explained. You dont need us to define who you are as a person, as you know that already.
There have been countless patterns of bad behavour in your life. You are on a destructive path and cant seem to break free.
I dont think you should tell your boyfriend about your one night with someone else, as you said you got drunk after a long period of managing without booze. You then had sex with some random guy, and cant really recall what happened during periods of blackout. Incidentally, the guy who you slept with is just as much to blame as he took advantage of you when you were pissed.
If your long term boyfriend doesnt understand by now your potential to self destruct or become overly possesive of him after 18 months, he probably never will anyway. But, you wil probably find if you did tell him what happened that night, that he will not be surprised. Because, your battle is with alcoholic abuse which leads you to act against your will. He knows that and he understands your family history. Yet, he still loves you. Maybe, when the time feels right in future, you may want to share your story with him. But, for now. it is time to start rebuilding your life and regaining self confidence and self worth.
Time is a great healer of destructive behaviour, providing you choose to believe that.
Begin each day by choosing not to hate yourself, as you said you do. Find positive things in your past to dwell on and learn to appreciate yourself more. For one thing, your boyfriend must think you are a special girl to remain with you after 18 months, which is a credit to you.
It is no use trying to undo the past story of your life as that will always be there. Start a new book instead. Reinvent yourself by taking massive action in a new direction. It may be a new job, University, friendships, career, a sport you like or a business decision. What about helping others who are just beginning with similar problems of BPD ? Your achievements could be just the motivation they need to start again.
It is not easy to appreciate ourselves when we have failed for the zillionth time. Failed again and again, repeatedly. But, this world is full of people who have come back from terrible hardships and trauma, and found peace. Its not easy, its very tough to change. But, I believe in you and am sure you can rebuild your life. if you stick with it.

Personally I wouldn't suggest you tell him. You'd only hurt him. If either 1) the guilt eats away at your conscience, either go write it down and chuck the paper/burn it. Or 2) break up with him.

If you happened to sleep with someone else again, you definitely need to end things.

Once is by accident, twice is on purpose.

Watch the latest episode of modern family, that’ll answer your question! In short, no. People overreact and can ruin great things, if it’s a mistake you regret and won’t make again, I don’t think you need to say anything for now. If you want to build your relationship more, do that first then confess. Don’t confess first because you’ll hinder the building of your relationship.

Personally I wouldn't suggest you tell him. You'd only hurt him. If either 1) the guilt eats away at your conscience, either go write it down and chuck the paper/burn it. Or 2) break up with him.

If you happened to sleep with someone else again, you definitely need to end things.

Once is by accident, twice is on purpose.

So if your partner cheated you'd bit want to know and if you found on further down the line you'd have happy they didn't tell you?

I'm almost 30 I too made this mistake.
I was 19 at the time stupidly drunk and too have mental health problems which did not help. I felt really guilty but didn't tell my partner, perhaps selfish but fact it would of hurt him, fact he would never of looked at me the same again and fact that would have broke me and sent me spiralling more. Instead I admitted only to myself I had screwed up and vowed to myself never to make that mistake again.
We have now been together for 10 years and have a 7 year old and we are the perfect family unit. Yes my mistake still lurks around in there somewhere and makes me feel guilty at times. I look at my family and do not regret my decision one bit.

Don't let people make you feel guilty or horrible about yourself. We are human, we do make mistakes. Also I know if my partner cheated on me as a one off, I would rather not know because it would destroy me in that I would never trust him again and I don't want to lose him. Continuous betrayal or an on going affair on the other hand is completely different, that's not learning from mistakes. So learn your lesson now and move on xx

and never date again?

I just feel like a lot of you are here to attack me when I have stated I know it was wrong. Im not someone who has planned it and has been going about it sneakily and doesnt regret it. I have woken up like oh ******** hell I have really messed up.

Issues or no issues have you not ever woken up with a stomach churning sense of dread ? I am devastated and I feel y'all just want to paint me as some cold unfeeling cow and not really offer anything I can work with

No I get that. I do want the opinions to fess up, I just feel like a lot of people want to tell me how *****y they think I am when that was never in doubt

As for your drinking habit, you've reiterated that all the avenues you've gone down haven't worked and you've given up on them, i get that. Are you Christian?

Yes how many times do I need to say that i get that point. I have accepted i know i have a problem and i did it anyway. Because I cant bear life to go smoothly. That is my problem I know and I am responsible. Why does no one seem to get that I do realise that?

My only concern is what will cause him more harm

I am not using it as an excuse. I was explaining the context of what happened, what I am like and our relationship and yes that second part is consructive thanks was considering doing that I am just worried about having a medical record of it

Repent.

Tell him, no offense but i think he has the right to know the sort of woman he is dating.

If i was your boyfriend, i would dump your arse in 10 seconds flat.

Alcohol simply isn't an excuse. You knew you would be at risk of cheating when drunk ect.

So if your partner cheated you'd bit want to know and if you found on further down the line you'd have happy they didn't tell you?

Yes how many times do I need to say that i get that point. I have accepted i know i have a problem and i did it anyway. Because I cant bear life to go smoothly. That is my problem I know and I am responsible. Why does no one seem to get that I do realise that?

My only concern is what will cause him more harm