I recommend reading "The Invitation" by Oriah Mountain Dreamer. This stanza is relevant to you:

It doesn’t interest me
if the story you are telling me
is true.
I want to know if you can
disappoint another
to be true to yourself.
If you can bear
the accusation of betrayal
and not betray your own soul.
If you can be faithless
and therefore trustworthy.
There is a difference between being self-aware, self-protective and having self-respect or being self-centred. That doesn't make you selfish. It means you are honouring yourself. You dont need to be a martyr to others' needs to be a "good" person. Sometimes saying No is the best thing you can do.