I don't think it's more author trying to make us pity the guy, but more of the reason he ended up being violent towards his partner. Like someone else said this feels like a character study, why the people are the way they are. There is no justifying what he did wrong, because u may go through abuse but that still doesn't excuse you being abusive in return.
Also I think u mean hayashida, the uke and not shuuna the seme. But I agree I wish there was some actual growth and communication between yumi and hayashida, but at the same time I feel it was better this way maybe, i wouldn't have wanted yumi to meet his abuser, and like hayashida himself says, I don't want yumi to forgive him.
Honestly speaking just like before when I read this it was selfish of the other guy who liked Shunna. If you knew he was beaten on Yumi what gives you the right to try to get any information about their relationship. And part of me still irks how the author trying to make us to pity Shunna after seeing how he brutally abused Yumi verbally , emotionally and physically just because he was being abused at work. And I wish he would’ve been communicating with Yumi instead of letting his anger out on him.