Well in this case theres nothing to forgive cos they aint bovvered!
The more you let it eat you, the more hurt and angry you will become and thats not healthy. How you move on? Acceptance. Accept that they have shit priorities and you dont. Accept that you cant change their actions as you cant control other people actions, just your own. Then concentrate on you and your actions and how you deal with the same situation and raise your glass to what a bloody better person you are

But what if that person is someone really important in your life?

be kind to yourself and allow yourself time to be at peace with whatever 'it' is. dont beat yourself up by thinking you should be over 'it' by now, or torture yourself with what might have beens or if onlys ... if its keeping you awake at night dont get mad with yourself; just think it through, write it down, read a book ... just dont let it get you down or rule your waking life - if you feel like its getting to you ask your gp to refer you for counselling.
one day you will suddenly realise that you are at peace with 'it' ...

sorry, for some reason i only got the first 10 or so posts in this trhead ... twas only when id replied that i got the full thread!

so if my post seems irrelevant ... i didnt know the full facts

Its still the same? You cant make them feel something they dont.....can you?

Can a person be more important than being happy?

IMO life is too short to bear grudges or go around with hate in your heart. We all do things in our life that we aren't necessary proud of and probably cause hurt and upset to others. Things happen in life, some of which you have control over and others you don't.

I am a great believer in forgive and forget - it is freeing to the soul. That doesn't mean that person has to be let into/back into your life - just to let those feeling go and move on.

Yes that sums up in the general "I've been wronged" arena how I feel about the idea of forgiving and forgetting: The inclusion of the: "hopefully you realise what you've done but you separately proceed along your lifes path and free from bitterness I'll proceed along mine".