I get that they were both meant to convey love, but to me it sounds too similar to be a coincidence that Rach and Tchaik both hear love as the same (especially that rising line in the violins). Why is this the sound of love? Did Rachmaninoff have Tchaikovsky in mind when he wrote his second symphony? Any analysis of the music would be lovely.
Tchaikovsky's influence was deeply intertwined with Rachmaninoff's life. They were contemporaries in Moscow; Tchaikovsky was already a renowned composer at the time (Romeo and Juliet was written 2 years before Rachmaninoff's birth), and attended one of Rachmaninoff's performances at the Moscow Conservatory when he was 19. It seems inevitable that he would reference Tchaikovsky, perhaps even in specific quote or tribute.
With regard to the specific pieces, I would recommend doing some research on your own. Find spots between the two that sound similar, and try to pinpoint the similarities. Are they melodic? See if you can sound out the melodies that both pieces share. Is it a question of dynamics, instrumentation? Challenge yourself to describe how Tchaikovsky or Rachmaninoff express love, or another emotion, and you'll find it easier to compare/contrast with the ways other composers do it, even in contemporary music.