I have been playing the violin for three years now. I have always wanted to play the cello as well but some musicians tell me that i should only focus on one instrument, otherwise, my bowing techniques would get mixed up.Someone please tell me!Is this true?What should I do?I really would like to play both instruments

My cello teacher plays both instruments quite well.
She says that once in a while she gets her bowing techniques mixed up when she is learning a new piece, but not often enough to be a big issue.
(By the way, are you sure "musically insane" is undesirable? "Sane" just means conforming to the current norms of the dominant culture. What's the fun in that?)

i dont think it is musically insane to play both insrumets. i play clarinet so i shouldnt be talking but my cousins all play bith instruments and theyre REALLY GOOD! so i wouldnt be 2 worried!

i dont agree with your teacher. i've been playing violin for seven years now and about two years ago i started playing bass and cello, so i dont think that expanding your instrumental abilities is such a bad idea. if you think about it, it could be better because it makes you think more about and work that much harder at those bowing techniques. sometimes teachers say that because they're worried you'll loose touch with the instrument you started out with, but if you're really dedicated to both instruments you'll learn to play both simutainiously.