In sims 3 pc, how come my new made sim cant meet or interact with my other made sim?

[venicen]

i've made a new sim which lives just beside my old made one. i was planning on making the two fall in love, marry each other, interact, etc. but how come whenever i play the new sim, i cant seem to interact with my old sim. i mean, this works in sims 2 but why not in sims 3? or am i just missin something? pls help.