What should I do about my two friends?

So my best friend and her boyfriend used to be really close. A few days ago she said she was gonna break up with him on the last day of school o he would have al summer to get over it. She also told me not to tell him. So her boyfriend sends me a text saying he is thinking about breaking up with her. He also told me not to tell her. Now, it seems like she is still in love with him. She said she felt terrible when she jokingly said "I'm breaking up with you!" and he took it seriously... Now she is freaking out over it. So I wanted to ell her not to feel bad because he wants to break up with her. He said he didn't want to be a douche about leaving her. I ,again, wanted to say not to feel bad. But, I promised them both I wouldn't tell them about each other's plans. Now that my friend wants to be with him again; I don' want to her to get hurt by being dumped. What should I do?