What do I do?

My fiancé’s mom is vacationing an hour from us and had invited us up for the day. My fiancé wanted to go but didn’t think he had the time with work projects.

My best friend texted me asking if we wanted to go out to a belated 30th birthday dinner this weekend. I speak to my fiancé and he says sure so I tell her yes. Figured we could do the dinner thing and he’d still have time for work projects. There was no day set.

Yesterday my fiancé’s brother asked if we were going to be home Saturday because this was his last weekend here before he leaves for a year to backpack/travel. My fiancé tells him we’d be here. I think his brother is planning a get together with friends(we live at my fiancé’s moms house) here and drink/hangout.

Today my fiancé asked when my friend wanted to do dinner, and I told him Saturday but I wasn’t sure the time. He tells me that he was between us staying home or visiting his mom but since his brother isn’t going to visit his mom, we’re staying here to see him before he leaves. Says maybe a late dinner would work but that he thinks everyone here will be drinking.

I find out a time from my friend who wants to do early because the restaurant closes at 8 and tell my fiancé the time. I make a remark about the 8 closing being early and he tells me it’s early. Doesn’t acknowledge the dinner time or say anything else about it. I’m pretty sure he doesn’t want to go.

I don’t know what to do. I could go myself but my friend would have to get me because I don’t have a car. I don’t know if I switch to next weekend when my fiancé’s brother will be gone on his trip?

My friend knows my fiancé’s brother and his friends yet my fiancé didn’t just tell me to invite her here, which would solve the problem.