Billy Hargrove is a stubborn, obnoxious boy. He doesn't like letting people know what's going on in his head, it's what his dear old dad taught him. But once he finally opens up, his attitude changes for the better.
Some would say that Eddie appearing in Billy's life was a good thing. Truly, Eddie helped him for the better, showing him what being loved was like. Billy truly loved it, more than anything. Eddie made his life better. He never realized why Billy treated him and the others like shit back when he was in high school. He helped deconstruct that, he built Billy back up, made him a better person. Until the gates opened back up.
Billy thought that the scars on his stomach were enough of a reminder of his trauma, but no. The bastard had to take something else from him, something he truly cared about. It could've been anything other than that. But no. He just had to come back and deprive him of one of the only things that makes him truly happy.
When he ran up to Dustin that day, he was expecting anything other than Eddie. Blood spilling from his mouth, the same it had done to Billy when he was rushed to the hospital. But Eddie couldn't be helped, he refused to be helped. So Billy stayed next to him, for as long as it took him to stop suffering. To die. He held Eddie's hand the whole time, he couldn't bring himself to let go.
The last thing Billy did for Eddie was kiss his forehead. That's all Eddie would let him do, he didn't want to see Billy in pain.
Billy helped Dustin up, letting him lean on his shoulder. He was barely keeping it together. Both of them were limping and there was no way Dustin could hold Billy body weight. The only reason they were both limping was because Eddie had insisted that Billy went before him so he couldn't stop what he was going to do.
There's nothing else they can do until the others come back.
Steve asked where Eddie was. Dustin couldn't form words, so Billy tried. All he could get out was a sorry before Steve had the guts to bring him into a hug. Billy leaned into it. That's all he could do, all he could bring himself to do.
Eddie changed him for the better and he was never going to forget it.