plsdonttellmybrother

My brother told me that he wants to end his current relationship. They haven't been toxic to each other, it's just that he has different interests and he doesn't think it'll work out. Neither of them are bad people, my brother still wants to remain friends with her (Though I don't know how long that will last). I've talked a lot with her too and she's nice to talk to, but I'll support my brother's decision especially if he thinks that staying will end up making things worse for the both of them. The problem is that my brother's gf is good friends with my current (and first) gf of about 4 months. I still really like her, but this will obviously make things a lot different to say the least. My brother said he's going to tell her tomorrow, which just so happens to be when me and my gf agreed to meet each other (I had not known about my brother's plans prior to planning my own). He's only told me about this and he doesn't want me to tell anyone else, so I am breaking his trust by being here, but I just don't know what to do. From here I see 2 options: 1. Don't tell my gf when I meet up with her, she finds out afterwards, and I look like an *** for not telling her (and possibly lie to her afterwards about not knowing about my brother's decision, but that's even more wrong). For the above decision, his gf contacted me recently about thinking something was off with him and I hadn't known since my brother and I only see each other on the weekends. So lying to either of them would seem less plausible. 2. Tell her and betray my brother's trust even more (even if I tell her to keep it a secret) I'm doubting whether or not our relationship will survive after the fact either way. Even though I would be more than happy to continue it, it's not only up to me to make that decision. I just want to know the correct course of action. If anyone knows any other possible option, I'd be glad to hear it.