Thank you for writing in to Just Answer.
I'm sorry to hear about the experiences you've been through.
Your decreased self-confidence could be at the heart of many of your problems. Including your dissatisfaction with how you look.
You are definitely not a bad or evil person for cheating on your boyfriend or kissing his brother when you had a fight with your bf. People are never bad, the behaviors that they often engage in are unsustainable ones. In this case, you likely already know that if you continue to cheat on your boyfriend he will find out one day and your relationship might end at that time. People cheat for many reasons. Sometimes it is an escape from the fighting and negativity of the relationship. Other times it is a way to feel good about yourself (that other people other than your bf like you enough to want you). So there could be many reasons.
I think what will be most helpful is working with a therapist to uncover all the issues that you are currently struggling with (low self-esteem, body-image issues, relationship problems, discomfort in meeting with people & bereavement issues among others). A therapist can provide a safe, non-judgmental space for you to talk about your problems and help you find solutions to steer your life in a positive direction. If you'd like to take a look at the therapists available in your zip code you can check out this directory.
I know you mentioned that meeting people face to face is hard for you. If that is the case you can consider talking to online therapists by searching for online therapy on the internet. But face to face therapy would be recommended in your case.
I hope that was helpful.
Please do let me know if you have additional questions/thoughts.