Byakuya had no idea how to be an actual good boyfriend

It really was a mixer of his lack of empathy, his ego, his self-centredness and never having a significant other before you, since you were the only person who could actually deal with him and his "I'm better than anyone because I'm rich and the ultimate Affluent Progeny" mentality

He knew he was a horrible person, hey he wasn't going to lie to himself because he knew he wasn't a good boyfriend as because of him running the Togami corporation, he rarely spent time with you and if he did. He always ruined the mood by saying something snarky or mean to you

Especially if it was something embarrassing like right now, You were on your period and you accidentally leaked onto your side of byakuya’s bed. Since Byakuya worked early he got up to see blood on your side. He shook you awake and said in a unamused and a bit annoyed voice

“Get up, care to explain why there is blood on your side of my bed?”