Someone I dated for a month or so suddenly blocked me everywhere and stopped all contact without giving me a reason. I tried reaching out multiple times, asked if I had said or done something to offend her, and even apologised without knowing what exactly I was apologising for, but she never got back. I have replayed all our dates in my mind, trying to find out what could have caused this reaction from her, and all I recall is her enjoying my company and having a good time. This has caused me a lot of stress since then, because I have begun to doubt myself and I don’t know if I will be able to feel better until I have heard from her and found out what went wrong. What should I do?
You should let things lie and absolve yourself if you genuinely believe you did nothing wrong. People can have their own reasons for behaving the way they do, and you aren’t doing yourself any favours by thinking badly of yourself. Your self-esteem will probably take a beating, and you are entitled to feeling upset by what has happened, but without any communication from this person, you are simply flailing in the dark. If she wants to get in touch, she will. If she chooses not to, for whatever reason, that is her prerogative. She has clearly decided to not be part of your life. If you cannot let go, and insist on her being part of yours, there will only be anger or pain down this path. I suggest you go easy on yourself and learn to let go of things you have no control over.

My boyfriend had a bad relationship before he met me, and he is afraid to commit even though I know he loves me a lot. How can I make him change his mind?
You can acknowledge what he has gone through, give him time, and simply let him know how you feel about him, until he is stronger.