Poor baby!
It wasn't really surprising that Steve reacted the way he did. Bucky could feel the tension, almost seething feeling coming off of his best friend and that hurt, but wasn't unexpected. The two of them had been all but joined at the hip for most of their lives up until the war. They told each other everything. Almost everything. Everything but one thing, but it was because of that they were here, now, having this tense conversation that was laced with regret and feelings that had been forcibly buried for the span of a lifetime.
Steve was coming at him about keeping his relationship with Natasha from him, and that wasn't fair. He'd not even gotten the chance to talk to her, and why shouldn't she have been the first one he spoke to about it? He'd wanted to, but the opportunity hadn't presented itself. Steve came to him in Wakanda, but she hadn't always been with him. He'd wanted to speak with her first, and find out if she just wanted to keep it in the past, a long forgotten memory, and let that be it. Or, if she didn't and thought maybe they had a chance to explore what had once been, then that was more complicated but something he could discuss with Steve after.
The more he let Steve's words resonate, the more they upset him. Especially when he thought about this place, and how things had been as opposed to how they could have been. Bucky's own fists had clenched at that point. He wasn't sure he'd ever been so angry with Steve in his life. "That's it? You're mad because I didn't tell you about a relationship I had with someone before I even got to talk to her about it?"
Bucky stood up, and took a few steps forward, off the porch. "I don't know, Steve. Maybe because I was in fucking shock about having been in love with someone and not having any recollection until I got up from an operation table. Maybe because I was trying to process it and the other multitude of memories I've been trying to figure out, balance between the good times and the horrific nightmares I have all the damn time about everything else I was made to do. And maybe it's for the same fucking reason you haven't told me what the fuck is going on here with you!" He reached back and all but tore the tie out of his hair so he could take his hands through it and take a deep breath to try to calm down.
It didn't work.
"I get here and find you living with a man who, last I remember, blew my arm off and told you to fuck off and said you were a disgrace. A man who would've just as soon killed me to get back at you because you lied to him. A man who let the government put your friends in a prison under the ocean." Bucky felt his eyes stinging. "I get here, and do you let me stay with you? No, you play house with him. He starts shit with me at the bar, I storm off and where the fuck were you? You didn't come after me, so I guess you went home with him. Did you even ask if I was okay? Why are you sulking like I owe you an explanation when you've left me in limbo for months?"