Story takes place over several years. Set up through the stages of grief. Steve & Bucky end up in Wakanda (T'Challa invites them) working through Bucky's trigger words, one at a time by figuring out underlying memories connected to each word. (Not solved by Shuri)
Multi, multi chapter. Extremely well written, but of course my brain cannot bring forth the author/title.
Pretty sure it was on AO3