Through the Line of Fire

Natasha and Steve have realized their attraction towards each other for a while now. They try being together but with Natasha's reluctancy to trust people and letting people into her heart they breakup. She keeps going back to him and he lets her in every time, causing a toxic relationship. Eventually he tells her he loves her and she can trust him. This scares her. After one night together she gets up and says she's leaving, this time for good. But, of course she comes back. This time with a secret.
Lies will be revealed, stories will unfold, and past hauntings will play a piece in this game.
What happens when one of them is faced with someone in their past?

Note: I don't own any of these characters or Marvel.
This is also my first fanfic so please just bare with me.