Hello, Hany. Korean language can be devided into two languages according to the listener. - informal form (for friends/younger people), and formal form (for stranger/older people) both 'saranghae' and 'saranghanda' are informal form. I think it's not easy to explain the difference between these two sentences for koreans though 'saranghanda' sounds a little more masculin, strong and stiff. and 'saranghae' sounds a little more friendly and usual. it's a matter of MOOD. just one different phoneme at the end can change the mood of saying. ~DAGO in 'saranghandago' is used to emphasize, repeat or quote something you(or someone) said. 'saranghaeyo' is formal form. sounds more gentle and polite, but usually it is used for older people or someone not close to you.