What is the evidence for the prohibition of obscene language, and is what is published on Facebook about love considered obscene?

It is not permissible for a Muslim to be foul-mouthed, for the Prophet, peace and blessings be upon him, said: "Indeed, Allah does not like obscenity or the act of being obscene." The Prophet, peace and blessings be upon him, also described "the vulgar, foul-mouthed person" as being among the people of Hellfire. The foul-mouthed person is one who is obscene in his speech, greets people with ugly words, and includes silliness and obscenity in his talk. Speaking about love between non-mahram (definition) men and women in forums is an ugly trait that falls under obscene speech.