This is the aftermath. This is a building, collapsed to the ground, a mess of rubble and settling dust. This is a Steve Rogers destroyed. This is a Steve gutted and warped by pain, made infinitely sadder by it, changed and made forever more desperate. Bucky saw that, began to feel it in the weight of Steve's stare, began to hear it in the words he didn't say.
Steve wasn't alone anymore and there was finally someone there who understood him entirely and perfectly, inside and out, beginning to the end of the line loved him, but that didn't make everything all better. Steve was still rubble; destroyed. And Bucky, with his intimate knowledge of pain and his wealth of knowledge of Steve Rogers, knew with a certainty that if he would do anything with the life given back to him, he would rebuild his best friend, build him back up from the ground if he had to, throw his arm over his shoulder and lead him, because thats what friends do and that's what Bucky knew best.
The guilt destroyed Steve, and the aloneness, but damn it all if Bucky wouldn't build him back up.