Betrayal is indeed far worse than rejection. With betrayal, you put your trust in someone and then that trust is broken. It feels like you don't know them anymore.
To be honest, I'm pretty bad at dealing with it. I'm decent at not exploding (although I sorta wish I would sometimes...). I tend to just cut contact. If I have to be around that person I act as though they don't exist. I don't give second chances, or at least, I can't remember a situation where I gave someone another chance.
That's in general. With love, I'm not sure. I like to imagine killing my darling then myself if they leave me- there's a drawing of two people stabbed through the same sword together that I find rather romantic and encapsulates this idea for me. In practice though, I can remember one clear time someone left me for another. We weren't physically together at the time and I was homeless so Internet communication was dodgy but I stayed faithful. She however... Anyway, once I found an account of hers I basically said I wouldn't get in her way and just wanted her to at least talk to me, that I couldn't live without that (I basically planned on slowly pushing them apart). After a few days of me considering things I realized how little she cared for me, decided she had never actually loved me, and left. I deleted my information about her, so now I couldn't find her even if I wanted to (bad memory).
Sorry for the long post, haha.
Loving someone wholeheartedly is way better than changing partners again and again
