cousins bf, cheating

my cousin and her bf live really close to me, let’s say her name is jane and his name is John.John is way older than her but pretty close to my age, he said we have more in common bc im more mature than she is to him. just adding that. well, at first i hated john, but we’ve gotten really close these past few weeks and the other night we got drunk and almost hooked up. j. we’ve been texting since it happened. im stuck bc idk if i should tell her, they both have told me seperately that they don’t see a future together. Jane said she plans on leaving him and eventually and he said the same. So should I tell or not? I feel like I shouldn’t because they’re going to breakup anyways and I don’t want to add more heartbreak. I feel guilty but then again not bc she cheats on him. Confused!!!

Update: wow. Y’all had some assumptions. I don’t want him and I told him that multiple times. I didn’t want him to try to have sex with me “we almost hooked up” means he tried to have sex with me.