Need advice

I’ve been friends with this girl since diapers and now we’re 22 . I met this dude and we were talking for a few weeks and we had sex . We weren’t talking about dating just talking . And I showed my friend his pic a few days ago and she’s like she dated that dude in 8th grade when he was a junior in high school and she’s like if I respect the sis code I’d stop talking to him . He told me they dated one month and kissed once but that was it. I kinda like talking to the guy and don’t want to cut him off . She’s like why is it so hard for you to let him go and she doesn’t know we had sex. She’s been dating a guy for 2 years so idk why it’s such a big deal to her . Then she added the father of my child on Instagram and been flirting with him . (He doesn’t know who she is) but I told him after I found out they were talkn ... Idk what to do. If it bothers her that much I’ll leave him alone but I don’t think it has to be that way.

He don’t know who who she is cuz we was private. She know who he is .