Thor:
You met at one of Tony's parties, you got to talking and tried some Asgardian alcohol, ended up getting drunk and fell asleep on his shoulder.

Loki:
When Loki attacked New York you were the only one who refused to kneel, it intrigued him as to how you could deny his order, yet still be so afraid.

Tony:
You had known Tony since MIT but you went off the radar after joining shield and ended up turning back up years later, when you got back you were hugged by Tony and asked many questions.

Steve:
You were a shield agent and were told to show him around, being the one to show him the new world after the world war.

Clint:
You were an old friend of his and after he disappeared you gave up hope of finding him. When he popped back up on the news you knew it was time to ask questions and so you did.

Pietro:
You were a secret agent in Hydra you had been there for months and had been trying to get information for Fury, you met him when he volunteered to be a test subject for them and watched as he progressed with his new found powers.

Peter Q:
He had been 'abducted' but you never lost hope you went out in search of him and eventually found him, after giving him an earful you joined the Guardians and helped them on their various missions.

Peter P:
You were a student at his high school, it didn't take long for you to be noticed as Tony Stark's daughter but you were found out too quickly for your liking.

Bruce:
You met after a failed mission he toon care of you when you were injured and soon enough you became good friends.