@saab,
Quote:If unfriend is a verb the sentence would be "He unfriended me" - sounds strange to me.
New collocations often sound strange. That's often what makes a foreigner sound foreign, Saab.
Quote:
Friend is a noun. Why is then unfriend a verb? We are friends. We make friends. We would not say "He friended me"
'unfriend' is a verb because English speakers chose it to be. Changing nouns into verbs is a very English language thing to do.
One day a situation might arise where "He friended me" will be said. Language, and the rules, governing its use are available to speakers of English to describe any situation.