when your ex bestie is dating your ex bf

I'm not saying my ex bestie is dating my ex bf but what if you where in this situation what would you do well ik I cried for 2 weeks and I regret breaking up with him but I want to fix our relationship but I haven't told anyone my sister is very worried about me I'll be fine my ex regret dating my ex I wanna forgive him but I just can't after what he did I feel like I'm getting  better everyday but I'm not sure but I'll do anything to have him back. But now  what would you do. Me and him dated a couple of months. I never really trusted him witch I should of cut her trusted me so now I'm all along so if your at a young age plz don't leave your  bf you might regret it and I don't want you hurt like me