Steve
[She takes her time with talking to the younger Bucky, and giving him a checkup. She can tell he's incredibly nervous about everything and she does her best to reassure him. She directs him to the lab down the hall for bloodwork and goes to talk to Steve.]
So I suspect you're right. He's definitely been through something traumatic. He wouldn't talk about anything specifically, but -- he did mention that his family died, in a fire. When he was younger.