Funny you ask that question, I was just talking about this to someone on here not long ago.
yes I believe God puts certain people in our life for a reason.
Sometimes they come into your life, and answer questions you never really knew you had, like messages coming to you, signs, they may not even stick around but when they do leave, something wonderful has happened. These are Gods Angels.
The others that stay in your life, have a reason also. They may be the ones God knows can be of help or you can help them along their path.
This is happening to me now. I believe every single person I have met on here, was guided to me by God. I know the reason for it, he has guided me to the message several ways.
Sometimes God puts evil doers in our lives, God sends them strong delusions, to see whether they believe the lie or the truth. He does this so (as Jesus says) he knows who to condemn. These evil doers are life lessons that God wants us to learn and guides us to the next path of his abundance and power.
They may learn from you and move on or choose the evil way, nonetheless God watches all and they will fall.