It is very hard - especially when it's your first hamster. There are various little things that can help cope, even if we miss them. For example one thing that is hard is the habit - feeding and checking on them every day - you go to do that and then remember.
I find it helps once the cage is cleaned and put away, and even to have a couple of days out or go away for a couple of days - so that routine isn't there hanging over you. On the other hand, sometimes it's too hard at first to deal with the cage. If it feels like that, then what I sometimes do is put a blanket over it. It really helps. It helps avoid seeing the familiarity that hurts, and it's a sort of sign of respect as well. Until you feel ready to deal with it.
One day you will just want it done, and that helps too. Having some kind of little ceremony or goodbye can help too - to move on and accept.
They are such precious little things that bring joy to us and become a special part of our lives. And we feel close to them - it's a grief like any other. It can help to think it was a good end, and in his own home. It is time really - in time you will remember the funny and happy things, once the initial feelings have past, and then they are happy memories.
And it's natural not to want another one just now - nothing will replace him. People vary in this - some people want to get another hamster quite quickly - maybe a different colour, sex or species so they are a different hamster - because they find it helps having another hamster to care for and love and makes them laugh again. And there are always plenty of hamsters in rescues needing a good home. Others find they need more time.
I actually keep two hamsters now. If one passes, the other is there that needs me and gives me comfort. It works for me anyway. Of course you still grieve over the one that has passed, but having the other one means I don't get the whole loss of routine or hamster life.