I don't know. I don't seem to grieve at all.
My grandma died 3 or 4 years ago (see, I can't remember when off hand). She and I were very close. But I don't really feel like I miss her. I think about her a fair bit, but I don't get upset. For the first month I often went to phone her to tell her something because I'd forgotten, but then I remembered and had a fleeting moment of sadness, but then it was gone. I felt cross with her for the first couple of weeks, but not that she'd died, rather that the night she died was one of the few nights she'd felt unwell and hadn't rung me! I couldn't have done anything, but she wouldn't have been alone, at least. But that was her choice and she made it for a reason, so I'm ok with it really.
My dad died about 18 months ago. The first month was hard, but only because his wife fucked off on a 3 week holiday the day after he died and left me to do all the legal stuff with none of the info I needed
and I felt I had to justify her decision to continue with the holiday... and my brother was angry with everyone (including me for just dealing with it) so he was as useless as a chocolate teapot and more of a hindrance than anything. He wasn't even neutral in it all. Oh and because 2 weeks afterward my dad died, I discovered my exH was having an affair...
6 months before my dad died, I went NC with my mother. I know some people 'grieve' after doing that. But I didn't. I was still angry with her for the things she'd done, but I didn't 'grieve'.
I haven't visited either of their graves. I don't feel the need to, they're not there. I needed to ask my dad a DIY question the other week, but he wasn't there, so after a moment of frustration, I went and asked one of the neighbours.
My marriage broke down, but I didn't grieve. I was fucking outraged for a few weeks, but within a couple of months I was over it and have been happier than ever for about the last 8 months.
I don't know whether I'm just hiding it all away and, at some point, it's going to come and bite me on the arse, but I've had counselling since (for other, early childhood, stuff) and it didn't bring anything up.
So I think everyone deals with it differently. I don't think there's any set way to react, you deal with it in the way that feels appropriate for you. Not in the way other people tell you you should feel/deal with it.
Sorry for your loss