what do you guys think?

i just found out that my friend’s sister is currently dating my ex, personally i don’t have a problem if my ex is dating anyone really but I was really shocked that he started dating her because i mean my friend’s sister we’re not friends but we’re acquaintances so i was really surprised but they’ve been dating for months and she knows that he’s my ex and we hang out together in the past so im kinda disappointed that she would do that and I also found out that she’s been hiding her post and stories in socmed from me, like I think she knows that is kinda off dating my ex when she know me personally to the point hiding their relationship from me. So am I the crazy one for feeling disappointed and kinda upset that shes dating my ex when he’s my ex already?