You say that you have a good relationship with him @Eveningonly but it sounds like it's surface level.
To an outside observer, I have a good relationship with my Dad. We go out for a pint every couple of weeks, go to the occasional gig or comedy night. And we have a nice time when we do. We catch up, have a bit of a laugh. But that's it, it's surface level.
You look at our WhatsApps, and it's just "Fancy a pint one night this week?". There's no chat on there, no engagement. When my Mum was alive we'd check in with each other daily, just because we'd have something we'd want to talk about., the same is true of my brother.
I'd never invite my Dad to Christmas, he comes because my brother invites him, but if my bro and family were away one year I'd just do a small family crimbo with DP and DD.
I don't trust him, I don't go to him to talk through issues or worries in my life. And why should I trust him. He treated my Mum like shit, cheating on her multiple times before finally leaving her when she had cancer. He had no time for me as a kid, weekends were for surfing or rugby, and as I wasn't interested in either, he wasn't interested in me.
He's now older, and lonely, and desperate for a better relationship with his kids. So we do the pub, and I give him the surface level, because I'm not completely heartless. But he's not my Dad, he's a distant relative at best. Had I gotten married, he'd not have been on the top table, he'd have been sat with his sister and family somewhere and I'd have resented his presence a bit.
I doubt your brother feels quite as badly towards you OP, but you probably don't feel quite like a sister to him. You set the tone of your relationship while he was only 11 years old, and so that's what he's reciprocating now. You can try to fix it, but it'll involve an apology, and some real effort. But I'd wait until after the wedding, because otherwise it just looks like your after a better invite.