Let me be more specific: I think that typical use of the English lexeme 'to betray' and its derivatives such as 'betrayal' has a defeasible implicature that the betraying agent acts intentionally, in particular with the prior belief that the betrayed patient, upon learning of the act, would regard it as one of betrayal. This, like nearly everything in natural language, is not a hard and fast rule, but I regard it as sufficiently probable that adding the adverbial 'on purpose' to the present sentence is pragmatically infelicitous in the absence of further context. Of course, others may disagree.
(See also a less jargon-filled statement of my position below!)
Your sentence sounds good, but my point was: is it possible to betray somebody unintentionally? I would argue that it is not. This nitpicking over semantics has nothing to do with the Vietnamese though (as far as I can see).
I do that all the times. Haha. One of the definitions for "betray" is "unintentionally reveal" or "to reveal unconsciously."
Someone might have told you a secret. Then in the excitement of conversations, one thing leads to another, and you accidentally reveal it and only recall it's a secret afterward. Unfortunately this happened to me more than once.
My feeling is that intent or (minimally) consciousness of wrongdoing is required at the moment of betrayal; accidental betrayal would not usually be designated 'betrayal' by a native speaker; another term or phrasing would be used. However, others may disagree, and it is of course the case that the Vietnamese 'phản bội' may have a wider semantic field than the English 'betray'.
Well, in the case I mentioned above, if my friend confronted me, I would say, "I'm sorry, I didn't mean to," and he might say, "No, you did. You were not simply a blabbermouth. You intentionally betrayed me."
You might want to watch the movie '4 Betrayals and a funeral"....or is it 'betrothals'?
Troi oi...language, so much more than reading a dictionary... Let me point you to the bard : "lo, he doth fart in the dark and thus betray where he is at" Macbeth 5:2
is it common practice to have an adverb (here cố tình) -between- the auxiliary verb (đã) & past infinitive (phản bội) ?