He doesn't deserve nothing of this lmao, he's just a bystander. Say he attacks the old man, wanna know what would have happened? Her family would have covered him, made the daughter say she is not pure anymore because MC was the one forcing himself on her... Results? MC having his future destroyed because some random hoe didn't had the balls to fight back, and she fuking has the nerve to act like her being done by the old fuk is MC's fault? Fk off.
If we take the old dudes words, this is not the first time he did that to her, and guess happened every time the next day after she got done that? Exactly, nothing. She never showed anything to MC. If he didn't catch them and started dating her do you believe this sort of relationship between the old fuk and her would have stopped? Ofc not since dude is family. So MC just dodged having his wife NTR by old man when he came from work and then discover his kids aren't his, but the old man's.
She just got off rails because MC saw them and now she can't fake being pure, she knows her future with MC is destroyed, so she forced herself on him to FORCE him to take her.
She's not a good person, neither is the MC, dunno about the gf but seeing how axx is this manga I expect something even worse from her, but the hoe that did the old man is by far the most manipulative disgusting hoe here.