why we choose the relationships we do

so why do we choose the people that we do??

i just stared thinking about this because i recently found out that five of my closest friends are all either depressed or on meds or something like that

im just wondering if we are attracted to people who we feel we have some connection with like we know that they can relate or is it random that i hang out with people that all struggle a bit in the same way

it was almost like de ja vu or however the hell you spell it but anyways
so one of my best friends had a bunch of cuts on her arm and i was like what the heck is that and she was just like ohh i scracted myself and i was like bullshit but i didnt say anything else untill another friend left but then we start talking about it and im just realizing that my other friend just had done some cutting and i dono

i think its interesting how all the people i gravitate towards are deep and umm err i dont know how to explain it otherwise but yea

so what are your thoughts?