REHAB= A rehabilitation centre for people with an addiction problem (drugs or alcohol)

I AIN'T GOT THE TIME= (coll.) I haven't got the time. AIN'T is the negative form for the verb "to be" and the verb "to have" in colloquial English:
- He ain't English= He's not English
- I ain't got any money= I haven't got any money
- I ain't no car= I don't have a car

HE'S TRIED= In this sentence, HE doesn't refer to her daddy (in the previous line), but to her manager (if you don't know the real story it's impossible to guess)

I WON'T GO= The form WON'T is the contraction of WILL NOT. The verb WILL may be used to express future or to express volition (=want), so the form WON'T very often means REFUSE. "I won't go" = "I refuse to go".

I'D RATHER= The phrase "I would rather" means "I prefer".

I'D RATHER STAY AT HOME WITH RAY= I prefer to stay at home listening to Ray Charles (a black singer she really admires), one of the creators of "rhythm and blues".

I AIN'T GOT 70 DAYS= I can't waste 70 days of my life in a rehabilitation centre.

CAUSE= because

Mr HATHAWAY= Donny Hathaway, a famous black American soul musician she likes a lot.

I DIDN'T GET A LOT IN CLASS= I have no class, no manners, no elegance (I wasn't born with it).

IT DON'T COME IN A SHOT GLASS= Using "don't" instead of "doesn't" is often heard in substandard English. A shot glass is a small glass designed to drink liquor. This sentence either means class is something you can't buy, or class is incompatible with alcohol.

YES, I'VE BEEN BLACK= Here, "black" is not referring to her race, because she is still a black woman, it is referring to depression, "black days", so it means "I've been depressed".

AND WHEN I COME BACK YOU'LL KNOW= Now YOU refers to her boyfriend: We broke up (you left me) and I got so depressed that I turned to alcohol, but you never knew how much your departure affected me. So if I go to rehab, when I come back you'll know how bad things went for me (and I don't want you to know).

THE MAN SAID (coll.)= "The man" is "the boss". The man here is the doctor at the rehabilitation centre.

I GOT NO IDEA= I've got no idea, I don't know.

GONNA= (coll.) going to

I'M GONNA LOSE MY BABY= I'm going to lose my boyfriend.

HE SAID: "I JUST THINK..."= That is her father talking, he thinks she has no drinking problem, just a little depression, that's all.

GO REST= in colloquial AmE the verb GO is often followed by infinitive without to, but in standard English this should be "go to rest", or "go and rest".

HAVE EVERYONE THINK= The complete sentence is "I'm not gonna have everyone think" (the first part said in the previous line), which means, I refuse to have people thinking...

I'M ON THE MEND= "To mend" is to heal, to repair. "I'm on the mend" means "I'm through a process of rehabilitation". She obviously thinks rehabilitation is for losers, for quitters, for people so weak they can't solve the problem by themselves, that's why she doesn't want to go there and she hates the idea of people thinking she's a loser. The idea is a bit stupid, that's why she says after this: "it's not just pride" (but, basically, it is).

'TILL= Until