He gets offended/sad when I dont want to shower together??

What do I do ladies?

My boyfriend and I have a decent sized shower. He really likes taking showers together and so do I most of the time. But sometimes I just want my time to just do what I got to do and get out. I don’t like fighting for more water, the way he just sticks it in me because he can, or that it takes twice as long. But he gets SO hurt if I say no. He says I’m rejecting him. I will sit in the bathroom to talk to him sometimes if I don’t feel like getting in again. I shower at night to wash the day off. Anyway, how do I get him to stop being hurt? I’ll say stuff like “not tonight but tomorrow morning? ;)” “I’m just going to be quick but maybe we’ll do something a little later 😋” but he still says I’m rejecting him. I can’t handle it.