<human>: Could you distill the essence of the text into 1-3 sentences?

my friend, lets call her stacey, broke up with my best friend 5 months ago, lets call him john. John's been devastated by this and its led to him seeing a shrink and taking some meds, and had to take a break from school for a semester. He's been a lot better now, but it's safe to say he's not completely over it. Stacey's been hanging out with a close friend of john's, whom I know too (lets call him jack), and it's led to them flirting around a lot and having an intimate moment in bed (just touching, no fingering or kissing). I'm best friends with stacey, and I've been telling her that it's not a good idea because if John ever found out Jack was doing this to his ex, it would be detrimental to his wellbeing. Now, do they REALLY like each other? I don't know if Jack does, but it seems like, knowing stacey, she more or less likes the idea of him or at least just really wants to have sex with him. So as stacey's right hand man, what advice should I give her? Because I can't understand how Jack could ever think it's okay to do this to his close friend's ex- I mean, they live together in university for christ's sake! So am I right to enforce this brocode policy, or am I being too harsh and it's not as bad as it sounds?
<bot>: my friend is in a flirty relationship with her ex's close friend. is this bad or not a big deal? The ex is also taking the break up pretty badly.