Your brain has the ability to help you recall a specific moment in which you felt hurt or betrayed (or anything else "negative") by someone you cared for: it serves you as a self-preservation mechanism, so that when you find yourself in a similar situation (according to determined patterns and schemas that help your brain store and recognize potential similar triggers), you "know" how to respond and act.
The point is that more often than not, your brain (that only wants to keep you safe) may even misinterpret situations by seeing threats where there's none (or not in such a way as it wants you to think): this happens because trauma's triggers often stay unprocessed and therefore your brain cannot really differentiate the whole spectrum of situations that you may encounter in your life.
Eg. someone is saying that they cannot come with you somewhere, and you may think they're abandoning you forever, while the truth may be they just can't (anymore) or don't feel well enough to or... anything else. It's not necessarily a permanent abandonment, and it is not something that has to be directly about you or "because" of you/your fault. Communication can help you understand better the situation and realize it all; but more often than not, your brain doesn't think about this option and goes full force into a negative mental pattern, especially if in the past you've had to deal with real abandonment. This is because your brain prefers to overestimate a potential threat, instead of not considering it as so (exactly cause it wants to save you, first and foremost).