Its my mates wedding and my girlfriend isn't invited and she is expecting me not to go?

Its my best mates wedding this saturday and my girlfriend is not invited because my mate cant afford it, meaning none of my other mates girlfriends are going but my girlfriend is not happy about it and is telling me if i go its over and she has contemplated killing herself. I really dont want to do cause i dont want to lose her but at the same time I cant let my friend down as he did so much for me last summer.Its causing me concern and I need help deciding what to do. I ve asked my friend if she can come back he said i really cant afford to do it mate the wedding list is full, but my girlfriend isnt excepting it. What do i do?