Syntax: 'Needless to say' is a discourse marker introducing something obvious. 'I keep her in check' uses the simple present for a habitual action. 'She was a bad-bad' uses the simple past 'was' to describe a past state, with 'bad-bad' as a noun phrase. 'Callin' it quits' is a present participle phrase functioning as the subject of an implied clause.
Morphology: 'Callin'' and 'Screamin'' (line 18) show the informal morphological process of dropping the final 'g' in present participles, common in spoken English and song lyrics. 'Wreck' is repeated for emphasis. 'Bad-bad' uses reduplication for intensification.

Syntax: 'Thinkin' in a bad way' uses a present participle clause to describe the subject's mental state. 'Don't know how that felt' is an independent clause with 'that' as a pronoun referring to 'took a big L'. 'Lookin' at you sideways' is another participle clause describing the manner of the main action implied in 'party on tilt'.
Morphology: 'Losin'' and 'Lookin'' continue the pattern of dropping 'g'. 'Don't' is the contracted form of 'do not'. 'Tilt' is used metaphorically as an adjective-like state.

Syntax: 'Unless I stuck by ya' is a conditional clause. 'Stuck' is in the simple past, which can be used in informal English for the past participle in conditional contexts (standard: 'Unless I stick by you' or 'Unless I had stuck by you'). 'You're the sunflower' is a declarative sentence with 'you' as the subject and 'sunflower' as the subject complement.
Morphology: 'Ya' is a colloquial morphological variant of 'you'. 'Sunflower' is a compound noun. 'Would be' uses the modal 'would' to express a hypothetical situation.

Syntax: 'I can hear you tellin' me to turn around' is a complex sentence. The main clause is 'I can hear you', with 'tellin' me to turn around' as a present participle phrase modifying 'you'. 'Fightin' for my trust' is another participle phrase describing 'you'. 'Even if we gotta risk it all' introduces a concessive clause.
Morphology: 'Gotta' is a contraction of 'got to', commonly used in informal speech to mean 'have to'. 'Risk it all' uses 'all' as a pronoun meaning 'everything'.

Syntax: 'I know you're scared of the unknown' uses an adjective clause introduced by 'that' (omitted). 'You don't wanna be alone' uses the contraction 'wanna' for 'want to'. 'But it's out of my control' uses the possessive pronoun 'my' and the preposition 'out of' to indicate a lack of control.
Morphology: 'Wanna' is a colloquial contraction of 'want to'. 'Unknown' is an adjective used as a noun (the unknown thing). 'Come and go' is a fixed binomial phrase.