I have lost two 'life' partners. I wasn't married to either, but together with each of them for ten years. The first died suddenly from a heart attack, the second from cancer a few weeks in to the first lockdown. Both pretty horrendous, but I knew second time round that I could get through it because I managed to the first time. The pain was much worse than when parents/grandparents died, because as someone's 'child' you have to expect that. I think I'm somewhat put off falling for another partner now though, as I don't want to go through it a third time!! - As I said in a previous post, I got through it by bawling my eyes out when no one was looking!! I think being able to do that, and not bottling it up or keeping it internalised really helped - everyone is different though, so it may not work for all.
As Erimus mentioned earlier in the thread, and John67 above, keeping busy is also pretty important in my experience.
A sad fact of life is that everyone you love will die..... unless you do first!
Good luck all