i have to tell my therapist on thursday that my wife sleeps with other men and im stuck on the sentence itself

m44, been seeing this therapist for 9 months for anxiety and a difficult work transition. we have a good rapport. he is mid 60s, dry humor, ex military, very straight presenting, not someone i would have picked for "kink/lifestyle informed" off a list, BUT he is sharp and i trust him. issue. my wife and i are in an MFM dynamic — meaning she has other male partners that i know about, that i meet, that i sometimes participate in setting up. i am into it. its not a "wife is forcing me" situation, its a "this is who we are as a couple" situation that we figured out together over the last 4 yrs. i have to tell him because for 3 weeks ive been hinting around an issue i havent named — one of her partners has been getting weirdly attached and its stressing both of us out and i NEED to talk about it w someone outside the situation. my therapist is the right person. but i have to give him the frame first. and the literal sentence is killing me. "my wife sleeps with other men with my knowledge and consent" — sounds clinical. "we have an open marriage" — feels like its underselling the specific dynamic. "im a stag, shes a vixen" — he will have zero context for that term and i dont want to teach him terminology in the session. "im comfortable w my wife having other partners" — feels distant. i keep practicing it in the car and every version feels either too detached or too defensive. and i havent even gotten to the part about why HIS specific dynamic — a kinda older quiet guy who i think might judge me silently — adds an extra layer of difficulty. the other thing is. it took me a long time to be at peace with this part of myself. i went thru 2 yrs of feeling like a freak before i found the community and realized im not. i dont want to lose that peace in a therapy room with one wrong reaction from him. but i also know the issue with her partner is bleeding into my work performance and i cant keep going without naming it. how do u guys frame this w a therapist who hasnt been onboarded yet. especially when the dynamic isnt just "open" but a specific kink-ish flavor. and how did u handle the moment after where they react — bc the 4 seconds of his face deciding what to think of me is the part im actually scared of