Mm. I think it’s time to talk to him. Maybe use the “I statement” method:
“I feel ____ when you do ____ because ____. I would like <insert expectation> to happen.”
For example, “I feel disgusted/crowded/disrespected when you leave your dishes in the sink for weeks because this is a shared space and is not being treated as such. The smell is distracting and I deserve to come home to a comfortable environment as we all do. I would like to see you clean your dishes within a reasonable time frame and leave room for me to use the sink as well. Are you willing to do that?”
Also Is there maybe a third person you guys share in common you could talk to about this with?