She isn't unwelcome. Steve doesn't blame anyone, but himself for the fighting. He planned this out poorly because he only factored in himself. He was ready to face Bucky. It never occurred to him to ask if they were. As a result things got bad in there.

He hates himself for being so blind to everyone else's reality. Mostly he's scared. As hard as he tries, Steve can't hide it. There's a faint tremble passing through his body as he lays down in bed.

"I thought he was someone else; that I was somewhere else." He explains as he closes his eyes. There's shame to go with his fear and self-loathing. It took so little to set him off again. Now Steve feels trapped in his own body again with hands grabbing at him and forcing compliance. It's stupid, isn't it? He knows that wouldn't happen here. It's not real, but his body isn't so easily convinced.