My boyfriend (28M) lost his brother and best friend. (31F)I'm trying to support him, but I'm starting to feel invisible.

My boyfriend's brother passed away suddenly a few months ago. They weren't just brothers, they were best friends. It has been devastating for him, his family, and everyone around them.

I've tried really hard to support him through this. I understand that grief changes people and that this is probably the hardest thing he's ever been through.
The problem is that I feel like our relationship has almost completely disappeared.

For the last couple of months, almost everything revolves around his grief, his family, his friends, and people who knew his brother. I understand why those things are important, but I feel like there is very little space left for me or for us as a couple.

A recent example:
I took some time off work so we could spend a day at the beach together. I was really looking forward to having some quality time with him because I feel like I've barely had him to myself for weeks.

While we were there, some friends of his showed up. Friends who also knew his brother. He had previously said he didn't necessarily want to spend the day with them.

At some point he went to say hi and came back over with them and said something like:
"We're going to grab a drink, are you coming?"
I said, very gently, that I had actually been looking forward to spending time together.

His response was basically:
"Well, I'm going anyway, so you can stay here on your towel for half an hour or something."
I ended up going, but I felt hurt. To me it felt like yet another moment where our time together was interrupted or pushed aside.
To him, it was just a 30-minute drink with important people.
That disagreement turned into a much bigger argument. Not because I do not support him doing things like that. It’s the nonchalant attitude that says “I’m going to do this, and you figure it out for yourself”

His perspective is that he feels constantly criticized. He says every time we spend time together lately, something becomes a problem. He feels like I don't understand how much he is struggling and how much effort he is already putting into the relationship while grieving.

My perspective is that I feel like I'm constantly making room for his needs while there is very little room for mine.
When we're with his family, I'm there.
When we're with his friends, I'm there.
When he wants to spend time with people connected to his brother, I support that.

But when we are finally alone together, I often feel like I only have half of his attention. We don't really talk. If I bring up something important to me, it feels like he's not interested or doesn't have the emotional capacity for it.

For example, we're going on vacation in two weeks. I'm excited about it and I'd love to talk about it, plan things, look forward to it together. He has no interest in discussing it and acts very casually about it.
That sounds like a small thing, but it makes me feel lonely because I'm realizing I don't really have anyone to share my excitement with.

Another issue is that I feel like I'm the only one initiating contact now. Sending good morning messages, starting conversations, trying to reconnect, asking to see each other, asking how he's doing.

I've reached a point where spending time together often doesn't feel enjoyable anymore, and that makes me incredibly sad because I love him very much.
The most confusing part is that when we talk about this, we both end up saying the exact same thing:
"I feel alone."
"I feel misunderstood."
"I don't feel seen."
"I don't enjoy our time together lately."
We're both hurting, but we seem unable to reach each other.

I don't think he's a bad person. I don't think grief has an expiration date. I also don't think I'm asking him to "get over it."

But I do wonder:
How much of this is normal grief, and how much is a relationship slowly falling apart?

How do you support a grieving partner without completely losing yourself in the process?
Has anyone been through something similar and found their way back to each other?