Syntax: This is a direct address ('My love') followed by a declarative sentence with an existential 'there is' construction ('There's only you'). The third line is a fragment, likely completing the thought 'the only thing that's bright,' which is a common poetic device in song lyrics for emphasis and rhythm.
Morphology: 'My' is a first-person singular possessive determiner. 'Love' is a noun used as a term of endearment. 'There's' is a contraction of 'there is.' 'Only' functions as an adverb modifying 'you.'

Syntax: Two parallel independent clauses with the same structure: 'You're every [noun] that I [verb].' This parallelism creates a rhythmic and emphatic declaration.
Morphology: 'You're' is a contraction of 'you are.' 'Every' is a distributive determiner. 'Breath' and 'step' are countable nouns. 'Take' and 'make' are present tense verbs. 'I take' and 'I make' are defining relative clauses introduced by 'that.'

Syntax: A complex sentence with a main clause ('I want to share...') and a subsequent independent clause that provides the reason ('No one else will do'). 'Will do' here means 'will be acceptable or sufficient.'
Morphology: 'Want' is a stative verb in present simple tense. 'To share' is an infinitive verb. 'All' is a quantifier. 'Will' is a modal verb expressing certainty about the future. 'Do' is a pro-verb substituting for 'be acceptable.'

Syntax: The first line uses repetition ('Two hearts, two hearts') for emphasis, followed by a relative clause ('that beat as one'). The second line is a simple declarative sentence in the present perfect tense, indicating a recent past action with present relevance.
Morphology: 'Hearts' is a plural noun. 'That' is a relative pronoun. 'Beat' is a present tense verb. 'As one' is a comparative adverbial phrase. 'Have begun' is the present perfect form of the verb 'begin.'

Syntax: A complex sentence structure. The main clause is 'I'll be that fool for you.' 'I'm sure' is a parenthetical expression of certainty. 'You know I don't mind' is repeated for emphasis, and ''cause' (because) introduces the reason.
Morphology: 'I'll' is a contraction of 'I will,' a future tense marker. 'Fool' is a noun. 'For you' is a prepositional phrase indicating purpose/benefit. 'Don't mind' is a negative verb phrase in present simple. ''Cause' is an informal contraction of 'because,' a subordinating conjunction.