bisexual boyfriend

so i found out a couple months ago my almost 2 year boyfriend is bisexual just like i am. i have no problem with it but i know that at some point he’s gonna wanna try sexual stuff with a guy. he says he isn’t interested in guys as in a relationship/in love just sexually. im super anxious about the moment when he says “ i wanna hook up with a guy” because thinking about him with anyone else no matter the gender is SUPER hard and it makes me cry. im an extremely anxious person so i cant get it out of my mind. i just had an anxiety attack and cried for hours about it with him. what should i do? should i break up and let him be so im not in the way of that? or should i be with him and live in the moment? i love him so much and i want more years to come, by his side. i know that if i stay i’ll be waiting and anticipating the moment he says he wants to hook up with a guy and experience that. i CANT be in the way of that because it’s selfish. he’s my best friend. please help :(