Songs stretch (and break) grammar rules. It's not wise to use songs as models of English.

I think this is not strictly grammatical, but (i) it is the way a lot of people talk, and (ii) it makes the song better.

They certainly cannot be ever used before.Read grammar.It will explain you everything about the sentence structure.

Hmm, nobody explained the reason. tender, sweet, and true are modifying the verb 'love', they are not modifying 'me'. Therefore, they are used as adverbs. However, they are spelled wrong. Note that almost all adverbs end in "-ly", so you can convert many adjectives to adverbs by adding "ly". * Grammatically the song should be: Love me tenderly, love me sweetly, love me truly. This is the imperative form of a sentence, like "Come here!", so the subject 'you' is implied. * There are exceptions! Such as fast. Adjective: fast car. Adverb: drive fast NOT fastly.