Welcome to the forum!
It's very hard for some folks to get rid of their monogamy-based societal programming. Even though they may have agreed to be open and honest, their habits don't reflect that. That is hard to change.
The poly dating dynamic is also very hard - finding the balance and not going overboard with NRE (even if the relationship is just in its fledgling state) - it's almost an "oooh shiny!" reaction and weaving a whole bunch of actions around that.
Hard for a partner to deal with, for sure.
So, if you don't mind sharing - have you been dating others?
"Listen, or your tongue will make you deaf." - Native American Proverb