Santaclaws I don't know if it will help but I am in a similar position. I believe there are many people who can relate but they probably aren't on MN.
Firstly you were right to ask why online man cooled off. You are entitled to know, his attitude would affect your life. Please don't beat yourself up about that.
Next, you are seeing your daughter tomorrow and that is a plus. You are going to your daughter on Christmas day, that is a lovely thing to be able to say, and it sounds like you have grandchildren too? That is precious. Just make the most of every minute you are with them.
Some people don't even have any family members at all, and have not been invited anywhere, so already you will be ok on Christmas day.
My sons also have their own families and busy lives [so grandchildren here too]. I saw eldest son last night and will not see him until Christmas day now....but it is lovely I'm invited and will enjoy every minute I'm there.
In the meantime I shall be very busy as I'm also getting over a deep betrayal and a friendship of 13 years in the bin. [Not a relationship but it hurts]. I have a plan for every day, maybe you could do the same?
I have something to do each day and evening until Christmas day: last minute presents, food shopping, wrapping presents, taking grandson to the cinema, watching a film at home, visiting a friend, treating myself to a coffee and cake somewhere then a walk to walk it off! I am meeting a friend on Christmas eve for a cuppa and a chat, going to a Christmassy church service on Sunday, having a takeaway curry one evening, baking shortbread for youngest son, taking DIL's birthday present round.....just keeping very busy, to distract myself. I just have so much to do, and I don't want too much opportunity to think about how badly I've been treated lately. The person does not deserve my energy and certainly won't be thinking of how I'm doing.
Can you also plan a holiday for next year? Treat yourself to a new book, a new dvd, plan a spa day, a day out, invite friends round one evening, bake a cake, try a new recipe, browse the sales etc. etc. Think of a new hobby for the new year.....Basically fill your mind with things that nourish and interest you, so your mind isn't full of online man. Your energy can go towards doing lovely things for yourself and pampering yourself in the Christmas break.
So make plans to fill your days, also plan to just relax and have a tipple/chocs and watch tv/film in front of a cosy fire.....you will be fine.