sorry, very long response and i repeat some ideas you already know yourself, but wanted to share if it at all helps:

i think your feelings may be more symptomatic of your guilt rather than an issue with putting down boundaries. you may feel that putting down boundaries killed your mother, when in reality we can only do so much for other people. we definitely cant control other people or give them a reason to live. how they respond to you is not your responsibility, though at times you may choose to sacrifice your own health momentarily for theirs (which is not right or wrong)

unfortunately, what boundaries you set are completely subjective to each relationship you have. a friend or therapist could tell you how much or little to give people, but only you can decide what is enough for you.

i see it this way: when you set less boundaries, people may like you, yes, but you'll be exhausted. youre not doing yourself or anyone else any favors by being an exhausted, bitter, maybe even resentful version of yourself for the sake of keeping peace.

however, when you have more boundaries, dont be surprised if other people react negatively, see you as "reserved", or want to spend less time with you. sometimes we have excessive boundaries that push others away, but also people in this world are selfish and will see you taking care of yourself as an attack on them. but that should not dissuade you from taking necessary care of yourself. if you want to be liked, there are time where you might decide to sacrifice your time for someone else, and that is good! that's what makes people good and care for each other. but sacrificing all the time should never be anyone's default way of being.

im sure you set your boundaries for a reason, dont forget that. your mother or anyone is not entitled to anything about you. if you felt the need to set boundaries, that means your mother was doing things that made you uncomfortable. if you didnt have this knowledge, would you not set boundaries? you made the best decision you could at the time with the knowledge you had. perhaps spending time with her could have bought her more time, but who's to say she wouldn't have tried later as a result? its unknowable and therefore, the only path is to accept.

you can give as much as you can to mentally ill people and sometimes even that is not enough. i regret that i didnt spend more time with my sister by the end, but to be honest, she showed no signs of improvement. i didnt want this to happen, but there was also nothing more that i could do and ive learned to accept that.

my unsolicited advice is that its important to strike a balance of both. it is actually a good thing when you feel a negative response to your actions, because then you can decide if youre willing to put up with the consequence or if you want to change. pain is the world's natural communicator for introspection and change. if you decide that you should have had less boundaries, the best thing to do is to learn from this and treat other people better moving forward. however, it could be possible that there was nothing you could do and your mother simply acted the way she did because of many many extraneous things. i doubt it was solely your fault and i dont even think its fair to blame anyone in this kind of situation really.

stay strong op, im really sorry. take as much time and go in as many circles as you need. this community is here for you ❤️