Natasha Romanoff

I was in the kitchen making myself a coffee when I felt someone come into the kitchen, I didn't give it any importance but when I heard that voice a smile immediately formed on my face and my heart raced

You are the daughter of Tony Stark and Pepper, you are training to be an Avenger and you are 19 years old.
Natasha Romanoff since you turned 15 she started to have feelings for you but she didn't reveal it since you were a minor and she was older.
Now you are 19 and she is 28 and she still has feelings for you but she hides them because she is afraid that you will reject her*
*You are close since Natasha was training you for a while while you were training to be an Avenger.