Hi Aud. I can't think of a situation in which you would say "betrayer." When referring to someone who has "betrayed" you, you can call that person a "traitor." Calling someone a "betrayer" technically wouldn't be ungrammatical, but it would be unidiomatic.

In one at least one version of the English Bible it says, 'here comes my betrayer'.

I guess traitor is mostly used as someone who betrays his country but betrayer is more like betray someone .

she has BETRAYED him. it's not generally used as a noun in this case. We don't often say "she is a betrayer!!" Nor is she really a traitor, though these can be used as labels when people speak in anger.

Traitor is often used more in a political sense to single out a Person or people who have betrayed their country for example. Betray, As a verb is often used more emotionally to talk about peoples relationships with each other. Example: I really trusted my girlfriend, but she betrayed me. ( she had a relationship with another guy!)