Feelings of rejection tend to be internalized feelings of insecurities. You can try addressing the insecurities to the point where you feel more confident… it is a start. But yes, dealing with the challenge of RSD is a process, often a painful one. Reacting emotionally is tempting. And it isn’t wrong to get it all out there either, but to protect yourself and others, try journaling your emotion, putting it away for a few days, then revisit it and see if you still feel that way. Most likely you won’t. The act of journaling tempers the rawness and can help sort out underlying insecurities.
(It also helps us find red flags and patterns in relationships, too.)