Main triggers - feelings of rejection 9stirring up older feelings of rejection), frustration/anger combined with feelings of powerlessness (ie you need to lash out, and the only person you can safely lash out at is yourself), feelings of self-disgust/humiliation.
It's hard to explain, but I used to have relationships (with friends and parent-figures and teachers and all sorts, not just romantic relationships) which were semi-destructive, too intense, and were all about me being needy and NOT getting my needs met properly. A bit like picking at a sore patch constantly, lurching from emotional crisis to crisis etc. The self-harming occurred during the more emotionally intolerable phases of those relationships. It was a pattern of behaviour which was almost entirely driven by me and which the "object" - the other person being targeted by all the crazy feelings - was quite often quite in the dark about how I felt.
How did you stop - I stopped it because I had some counselling (not enough, but some), made some firm non-dependent friendships and stopped abusing drink/soft drugs/other people. I started slowing down, emotionally/job-wise, taking more care of my own feelings in relationships and experiencing day-to-day knocks for what they were rather than as some sort of hideous replay of old hurts, IYKWIM. I think some of it was just maturation, really. I was about 22 when I stopped actively self-destructing, I think.
Did you want to stop - I didn't want to stop for quite a while, it felt necessary, like emotional blood-letting. I wanted to stop beiong found out and I wanted to stop experiencing the disgust and shame I felt after I had self-harmed. I did eventually start to make the connection and realise that it was an all-round bad idea (sounds thick but there it is)
Can you stop without help - I don't think you can stop without help, no. I tried over and over again but just found myself hitting a brick wall and ending up at rock bottom again. I did accept help in the end.
How long did you do it for - I did it from the age of 5-ish (deliberately biting my tongue to draw blood in class, for attention, making big scratches in my arms and showing them to people etc) through the teenage years (cutting/burning etc) until I was about 22. The last time I self-harmed I went a bit further than I had previously and permanently scarred myself. It frightened me enough to make me really seek proper help, plus I was in a good healthy non-fucked-up relationship by then.
I don't think I will namechange for this, because it's the past and I've given up feeling low and shameful about the past. I really, really hope this helps, whatever your reasons are for asking these questions. You would be more than welcome to CAT me if you wanted to.