Till It Bleeds Daylight.

Steve has been undercover with Hydra for a couple of months, slowly getting deeper into the organization . As he tries to figure out what they're plotting and tries to take them down, he struggles with his past, loneliness, and keeping his cover. When he finds out about a mysterious contractor, the Winter Soldier, Steve figures he or she is the key to Hydra's plans, but getting more information is not without risk. But well, Steve is anything but risk averse - just ask his secretive one-night-stand turned regular hookup turned ...something, James "Bucky" Barnes.

Or, going undercover with the criminal organization that haunted your neighborhood growing up, a Steve Rogers guide:
Step 1 - Don't make it personal;
Step 2 - Don't take unnecessary risks;
Step 3 - Don't lose your cool;
Step 4 - Don't fall in love with a hitman;
Step 5 - Ignore rules 1 to 4, especially 4.

Title from the song "Lovers In A Dangerous Time"

(THIS STORY IS NOT MINE!! IS FROM AO3. THE AUTHOR IS "cable-knit-sweater (cable_knit_sweater)". THIS IS FOR THOSE WHO DOESN'T KNOW HOW TO USE AO3!! AGAIN THIS IS NOT MINE!!!!!!)