The man retreated to his bedroom. Not the actions of someone attempting to protect a beaten woman.
Perhaps, but...
1. By retreating to his bedroom, he drew the attacker away from the woman and also gained access to his gun.
2. By locking the bedroom door, he prevented the attacker from taking the gun from him as he retrieved it from its storage place.
3. When the attacker broke into the bedroom, he had clear-cut justification for a self-defense shooting.
I'm not as certain of his intentions as you seem to be.
By retreating and locking the door, perhaps knowing the abusive fellow would come kick the door in, he set the stage to eliminate the threat once and for all --and without legal repercussions. If this was a pattern of behaviour between the deceased and his spouse, the odds are good that the deceased would finish dealing with (abusing) her later and pursue the guy.
He drew him off, and in such a way that he could finish it.
Whether that was his intent, or sheer flight was, the result is the same.