Tradução - Japonês-Inglês - Kimi o ai shiteru ... Watakushi wa anata wo ai...

Just in case you didn't GET it, the FIRST time? @_@
All joking aside, someone is playing at "practicing Japanese" here. The first "I love you" is informal, and uses one style of romanization; the second uses quite formal Japanese (and therefore sounds a little strange to modern Japanese ears, because of what's being SAID), and also uses a different romanization style.