I know this all too well, although for me it surfaces much less as the thought of “saving myself the pain”, but instead being a very aggressive: “I am so bad/worthless, any attempt by me could be genuinely hurtful/transgressive”.

Had a lot of work, therapy, life developments, it got better, but never truly vanished as this thing that sometimes bubbles up at the core of my self - some days more, some days less. Wishing you the best in your own struggles with thoughts and feelings like that.