B Story: The "Love" Story
Now that you've reached the second act of your script, it's important to have your B Story at least 30 pages in. In some cases, the B story is hinted in the first act, but isn't official until the second act. Like for example, in Aladdin, in Act 1 we see our protagonist, Aladdin first meet Princess Jasmine in the marketplace, but the B story doesn't officially begin in act 2 when Aladdin meets Jasmine, disguised as Prince Ali. From there we can see their love begin to blossom.
Some might think that the B story is always the love story, but in other cases, the B story can be a subplot. It's important to note that whether you have a B story character or a B story subplot, near the end of Act 2, the protagonist has to either lose the A story or the B story, and in some cases, it's usually the B story that fails. But more on that later. Let's take a look at some B story examples.
In Frozen, we meet Kristoff as Anna's love interest. Sure he doesn't look like royalty, but he is the driving force that helps Anna on her quest. It's important to note that when you have a B story character, they need to be like a mentor to the protagonist. During the journey, he advises her that she can't marry someone she just met and even fights to protect her from a pack of wolves and a giant snow monster named Marshmellow made by Elsa (which doesn't happen until the One Hour Turning Point also known as the Midpoint.)
In Liar Liar, the B story follows Fletcher's relationship with his son Max. From this point on, it's a battle between family and work which raises the stakes a bit. If he wins the case, he could risk losing his son in the process. As a viewer, we then begin to ask ourselves how he is going to able to keep both? During the second act, we see Fletcher struggling to balance the court case and spending time with Max before he moves to Boston with his ex wife.
Finally, in The Wizard of Oz, although the characters Dorothy meets along the yellow brick road (the scarecrow, tin man, and cowardly lion) help her meet the wizard, the real B story character of the three is the scarecrow because just before she's about to click her heels to go home, she says to the scarecrow, "I'm going to miss you most of all."
Hopefully these examples provided some extra guidance for your script. Just note that sometimes, it's okay to give a hint of the B story in the beginning, but don't make it official until the second act. Once again, going back to Liar Liar, we see the loving relationship between Fletcher and Max from the beginning. We learn from their interaction that, although he's divorced, he still has love for his son and wants to be there for him. However with the court case standing in his way, he hasn't had much time to spend time with Max and puts work first, which dampers their relationship a bit.