I would think Hosty was nice to Marina the first time he went to see her but then exerted his power and threatened her if she didn't report on her husband LHO. That would certainly be enough to anger Oswald to that extent. It would also explain her avoiding speaking to Hosty after her husband had been killed.
Why do you ask how did Marina get Hosty's number plate? It was in Oswald's book. Oswald was involved in low level intelligence so he would be conscious if anyone was watching the house and would have noted the number plate. Maybe he did that to check with Warren de Brueys who Hosty was? Oswald was likely an FBI informant. Maybe that was kept from Hosty at first?
Abuse of power by Hosty could have led to relations with Marina but I think threats about deportation more likely. They certainly worked after the assassination.
That would certainly be enough to anger Oswald to that extent. Lee became very angry when Hosty was introduced before the interrogation began. I don't know what Lee said to hosty but I caused Fritz to tell Lee to calm down, and ask Lee why he said that to FBI agent Hosty. Lee told Fritz that Hosty had accosted his wife....
