I don't "check" with my boyfriend before I shower
What do you mean by check? Did you do this with someone before?
I was in a shower stall in an in-door pool in high school.
You shouldn't need to check in with people for using the shower. You should take responsibility for your own safety.
Yeah. Why do I need to check in? It's unncessary after all.
True, I'm sure you and your boyfriend are mature enough to let each other shower alone without needing to check up on each other. It may be sweet, but both of you need to have a healthy amount of privacy.