It's completely natural to feel guilty about not spending more time, or not going to this or that and it can be hard to get over that but it's also just life and it would be unhealthy to treat each time you see someone as if it might be the last.
With my dad, he picked us up from the airport after a trip to see my in-laws and he was already ill but had refused to go to the hospital because he "had" to pick us up. It was typically him, but you know, we're adults and would've managed! The next day I had an operation and got an infection which meant I wasn't as on the ball as I could be. I phoned him and he sounded worse and so got my mum to check on him (she'd moved out a few months earlier) but he was completely stubborn. Anyway, he did end up in hospital with pneumonia and I was feeling rubbish from my infection so I didn't even call, just sent him a smart arse text message about getting people to look after him. A few days later he took a turn for the worse, had to be resuscitated and was in ICU where he continued downwards. They told my mum and sis that they should just stop the meds and let him go as he was going anyway, but they refused till I could be there the next day to be with him. But I had loads of guilt, like I should've made more effort to make him go, that I shouldn't have canceled my operation earlier in the year so I would've been well and I probably would've called an ambulance for him whether he liked it or not, or I would've maybe called him more frequently. I guess a mix of I could've averted it (but who knows) and guilt that I didn't talk more and my last communication was an everyday silly comment by text.
After it all though I ended up reflecting on how easy it is to avoid dealing with death these days (if we're lucky and I consider I am given how few people close to me have died) and that's before the whole issue of the body coming up. No-one else around my age I know has seen a dead body and so it can be quite isolating as it's kind of taboo.
And then you wonder if you're boring people by keep talking about them!
Back when my Nana died none of us really spoke about it because we would cry and didn't want to upset each other. But that can be quite isolating and I would say don't be afraid to talk and cry to your family if they're the kind of family you can do that with. Thankfully with my dad I'd started going to church and so I had my vicar to talk to and obviously he'd had plenty of experience with death and the bereaved. I admit tho, it was good to cry to someone who wouldn't then in turn start off crying!