WHAT IS THIS BS!!!

SO... ive been playing league now for about 3 years and i remember how good this game was, it was fun, people where nice, good matchmaking, etc. but new i feel that all this has gone missing, in ranked i feel like im playing like a god and making the world rotate the way i want, but then i look around me and see that im the only one who is winning, no one thinks before going in on my team, and if the nemy team is getting first blood i have to deal with flamers (every game) the rest of the game, i feel like its me that is doing something wrong when i get matched with acid and trolls.

so now i wanna know, exactly(not all that smart bs) how the matchmaking system worsk because i feel like riot has taken me and put me into some kind pit full af acid and trolls, so tell me why am i getting matched with such mean people?