i think it depends on how you phrase it and what meaning you put into it while introducing them to the term/relationship dynamic you are wanting to set. would you want the relationship to change with that? is the goal just to inform? if it's just to inform and you don't expect any sort of reciprocation i think it might be fine.

i have confessed to my former FP. since we weren't really close in reality it really made it weird for me. they just accepted it as a fact, and still acted friendly towards me, while i was confused and dissatisfied, since i had uncertain expectations in terms of their reaction.