Most of the fic is pre-relationship, and is a post-Winter Soldier study from Bucky's POV. He's having trouble coping with what he did during that time and isn't allowed to live away from SHIELD HQ alone, and he and Steve are sharing an apartment off-campus. He has to go into SHIELD or Avengers tower while Steve is away on missions. While he loves Steve, his overbearing concern for Bucky makes things worse sometimes, and the fact that he's being pressured to make a choice between remaining heavily guarded indefinitely or joining SHIELD, who he's not a huge fan of, irritates him a lot. Steve is keen for Bucky to join the Avengers but Bucky keeps shooting that idea down. I remember him being quite bitter and sarcastic for a lot of the fic.
At the end, Steve is called away to another mission, and Bucky is quite snippy with him before he leaves. Bucky spends the fight at the Avengers tower, and gets JARVIS to pull up security camera footage on Steve so he can keep an eye on him. A building collapses with Steve inside and Bucky freaks right out, and when the Avengers return to the tower with Steve in tow, he lays a kiss on him in front of the others. In the end, I think he decides to join the team in order to keep Steve out of trouble.
If anyone could point me in the right direction I'd really appreciate it! I think it's a multi-chapter fic, but I could be wrong.