In tabletop RPGs, "session 0" has become a phrase to represent spending the time to talk about expectations for a game. What's cool, what's not, etc., so that players are expecting a similar experience. It sounds to me like you might benefit from something similar. If there wasn't that prior understanding, how is your RP partner to know this is important to you?
Any time I RP (Which isn't really much these days) I always try to make it clear from the get-go what I want and talk to the other person(s) about the sort of "Story Arc" so there is general idea in mind, Of course we leave out details like reactions and such to avoid spoiling the fun, but we'll often say something like, hmm, for example lets just use a silly scenario like rping about being little, if I know I'm going to want a diaper change in the rp, I'll say that at the start, maybe give a time/place for that to take place, something all parties involved can agree on, and I'll also want to clarify with said people if its wet, messy, both, or just a change for the sake of a change, and also clarifying levels of possible sexual additions into the rp.
That said I really only RP with one person these days, and I barely do that anymore due to time constraints and lack of privacy at home where my computer is to actually rp with them, but we've known each other for a while so we both know what is and is not okay, so I recommend if you like to rp frequently find a partner (Or small group of friends) to RP with, that way you only really have to do the get to knowing bit at the start, and once you get past the first few RPs it's just natural to know limits and such.