RIFF: When you're a Jet, Let them do what they can, You got brothers around, You're a family man! You're never alone, You're never disconnected! You're home with your own-- When company's expected, You're well protected!
The Jets define themselves by loyalty. It's more than just sticking up for each other. Loyalty makes them strong, and gives them a level of power and control over their lives that they couldn't hope for otherwise.
RIFF: Now I know Tony like I know me, and I guarantee you can count him in
Riff's counting on Tony, even though he hasn't asked Tony whether he'll back the Jets' in the rumble or not. Even though he's out of the gang, Riff knows you're a Jet "till your last dying day." It's not like Tony's going to fall in love with the sister of the head Shark or anything, right?
RIFF: Four-and-a-half years I live with a buddy and his family. I think I'm digging a guy's character. Boy, I'm a victim of disappointment in you.
TONY: End your suffering, little man. Why don't you just pack up your gear and move out?
Here's some insight into why Riff and Tony are so close: Riff's lived with Tony's family for four and a half years That suggests that Riff doesn't have any home life of his own to speak of, which makes Tony his brother in every way that counts.
RIFF: Oh, well now you're talkin'. Oh man, without a gang, you're an orphan. With a gang, you walk in twos, threes, fours. And when your crew is the best, when you're a Jet, you're out in the sun, buddy boy. You're home free home.
TONY: Riff, I've had it.
RIFF: Tony, Tony, look at me, will ya? Come on, look at me...Now, I never asked the time of day from a clock, did I? I never asked nothin' from nobody. But I'm askin' you: come to the dance tonight.
More trouble in paradise here, as Tony isn't quite willing to stand by his loyalties as a Jet. Riff has to appeal to their shared history in order to get him to come around, suggesting that Tony might not, in fact, be there for the Jets the way Riff promised.
TONY: I ain't playing anymore, can't any of you get that?
Tony's being pulled apart, and just like his friends don't understand why he won't help them, he can't understand why they don't want him to just be happy with his girl.
ANITA: A boy like that, -- Who'd kill your brother, Forget that boy and find another!
This is perhaps the biggest test of Maria's love for Tony. Not only did he kill her brother (accidentally, yes, but still), but Anita's pretty much saying "dump him or we're through." Maria's losing the loyalty of everyone around her, and yet she still stands by her man.
ANITA: One of your own kind, stick to your own kind!
Anita has good reason to blame Maria for loving Tony—he just killed Bernardo. But she pulls out another reason: loyalty to their own culture. Nothing but trouble when you fraternize with the enemy.
A-RAB: Lay off of him.
ACTION: Mind your own business.
A-RAB: Don't start up on me, or I'll punch in your stupid...
ACTION: You'll do what? Huh?
With Riff dead, the Jets' former loyalty to each other starts to fall apart. That means they'll be easy pickings not only for the Sharks, but for the cops as well. It's up to Ice to pull his crew together.
ICE: Now you all better dig this and dig it good. No matter who or what is eatin' you, man, you show it and you are dead. You are cuttin' a hole in yourselves for them to stick in a red hot umbrella and open it. Wide. Man, you wanna get past the cops when they start askin' you about tonight? You wanna live in this lousy world? You play it cool.
Ice takes control of the gang here, asking for loyalty in the name of survival. They all want to get even for the death of Riff, but if they don't put the Jets first, it's only going to get them arrested.
TONY: I… I didn't believe hard enough.
MARIA: Loving is enough.
TONY: Not here. They won't let us be.
MARIA: Then we'll run away.
TONY: Yeah, we can.
Once Tony falls for Maria, his commitment till his last dying day (literally) is to her and whatever life they think they can make together.