How Do I Say, I Love You Forever And Thank You For Everything In Japanese?

These are simple, I love you, which with proper pronunciation can convey for every would be.

Daiskui Desu, or Watashi mo Aishiteru. ( broken down they would be said,  Da (e) Su Ki De Su,
or Wa ta shi mo Ai shi te ru.)

Thanks you is much more simple, to say thank you which conveys everything in proper japanese would be. Domo Arigatou Gozaimasu. ( broken down it would be pronounced do mo ari ga to go zai ma su), Said sincerely and with a bow will convey the proper message, its also helpful to pick up a phrase book for such things, there are many out there that will teach you say simple phrases phonetically to get the message you are trying to convey across.