unironically i think that this is a large part of why i am polyamorous ... i just have seen many times in my life how people enter monogamous relationships in the belief that "this will cause stability in my life", only to see their heart ripped out of their chest some time later.
what people don't seem to get is that humans aren't machines. there's no "proof" you can do that somebody will never leave you. there is no "reliability" in monogamy, and "promising" to stay together for a lifetime doesn't actually do stuff. and anyone who has taken a statistics course, will tell you to never put all your eggs into one basket.
and that's i think a large part of the reason why i could never never ever be in a monogamous relationship.
edit: sry i know this doesn't help you at all in this moment. i'm just saying it because i get really angry every time i see people feeling like shit because these things happen. and i've grown accustomed to thinking that it's because of the really unnatural kind of relationships that are forced on people by the kind of neurotypical mindset ... idk i'm maybe spiraling but it's important to me.