I'm really glad you are here opening up. I, too, struggle with wanting approval and bottling things up. You sound really brave and self-aware and I commend you for your courage. It's totally understandable that you are struggling with feelings of abandonment and recognizing that you may be taking things personally can help with healing core negative beliefs.
I believe you are a loyal, kind person who would be wonderful to have around. Not everyone will always see that. Yes, it's great to work on ourselves and be the most confident version of ourselves that we can be. But, even then, some people just won't click with us or appreciate us. It's something that everyone struggles with. Some friends are only there for a season and a lot of people (even without mental health struggles) find it takes time to find a few true friends. Romantic relationships can also be short term for a lot of people and it can be a challenge to find the right person with character. Maybe it's worthwhile to keep in mind that it's not always about us. Sometimes, it's the relationship or the other person's issues.
I spent several years in a marriage where I tried to twist myself inside out trying to please my ex so he would be faithful. But, he never appreciated me for who I was or loved who I was (only what he wanted to change me into). Over time, I started to see there was nothing I could do. It is common for someone who is that unhealthy to cheat, lie, gaslight, make excuses, emotionally abuse, blameshift and make you feel like you're defective. But, the truth is they have issues and often simply won't appreciate you no matter how many hoops you jump through. People like that need to go because you can do better.
Maybe it would help to visit those who are otherwise forgotten and in need of companionship? Like elderly people in a care home (at least when things get better and they're allowed visitors). There are lots of lonely people out there who would appreciate such kindness and companionship.
I don't know if you have a faith. Sometimes, that helps me.
Have you ever tried Dialectical Behavior Therapy? I'm currently working on both Cognitive Behavior Therapy and Dialectical Behavior Therapy. Dialectical Behavior Therapy, while originally designed for people with borderline personality disorder, can help anyone with overwhelming emotions. I have a DBT self help workbook I'm going through while also in therapy. It has a section on interpersonal effectiveness (social skills and assertiveness training) that may help with relationships. I tend to have a very passive style where I try to people please and then the relationship hurts too much so I either want to blow up or run away.