How do I know when to use infinitive 다 form when speaking very casually to someone?
So in a TTMIK book called Real Life Conversations: Intermediate two close friends said to each other over the phone:
A: 아, 그렇구나. 그래야겠다. 조만간 다 같이 한번 보자.
Oh, I see. I should. Let’s meet up all together one of these days.
B: 그래. 한번 뭉치자. 본 지 진짜 오래 됐다.
Sure. Let’s get together. It’s been a really long time since we last met.
Particularly in the last sentence of what person B said they used the infinitive 다 form of the verb 되다. Does it make any difference in meaning when keeping it in this form? Does it show that you’re saying it to yourself? How do I know when I can use this form in casual conversation? And does saying a causal sentence like this in the infinitive form add any underlying nuance to the sentence?