Boyfriend invited to wedding

My boyfriend of 2 years was invited to a wedding of his really good mates. The invite was more of a save the date so official invitations haven’t gone out yet. He said it’s just a really small wedding, and that’s all he mentioned. I’m not sure why I thought partners were generally included in the invites, but is that a thing? Do people automatically bring their partner?

He’s done this before with parties saying it’s a small space and not inviting me, but then later I’ve seen pictures and there have been other girlfriends at the parties.

I know it’s up to the bride & groom, but are partners included in the save the date/invite memo? I haven’t been to a wedding since I was little...