Eeek help me?!?!?

my mate (known her for 10 years, very close) had a bf over 5 years ago and she left him. me and him are now mates but shes realy upset about it! i didnt think shed mind after all these years hes nothing to do wiv her shes engaged now.what do i say to her? we get on well but i hate getting in the middle of their problems! help me