Does anyone else feel “bad” for standing up for themselves?

I have issues being brave to stand up for myself and voice my feelings in a somewhat “demanding” manner. I’m known as the “nice one”, and because of this my friends or people around me can boss me around and insult. I blame myself for this. Recently a friend crossed a line and there’s no way I can forgive her for what she did. She was super rude to me and still calls me so she can vent about her problems. I told her I need space and how I feel disrespected but she isn’t listening. She apologized half heartedly and expects me to be okay with that. She keeps calling and I keep ignoring, then she’ll message and say “I said I’m sorry”. It’s a cycle with her, she will never learn. She drains my energy and makes me feel anxious and I need my space away from her. I wrote a message but I don’t know why I can’t seem to press send! She did me wrong and I’m the one afraid to stand up for myself. Any advice on how I can stop being so stupid lol?
Updates
10 mo
Update: I took your advice into consideration and did in fact tell her my feelings. I also put an indefinite break to our friendship. Tbh I don’t see it nor want it to ever continue. I haven’t blocked her but I will not hesitate to if she keeps harassing me. I wanted to stand up for myself for years and now was able to. Thank you for your advice 😊
Does anyone else feel “bad” for standing up for themselves?
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