Am I Being Stalked? Any Advice? Or It's Nothing To Worry About?

We have a neighbor who moved next door 2 years ago. He has his friend clean up and help him out with his property. I see no problem with having a friend help out, but his friend is an older man he is at least 45 or older. The part I don't get is he is there every weekend with his truck parked right out in front of our house view, yes he can park there because it is their property. It's common curtisy when we ask him nicely to park about 10 feet out down out of the view of our house(In their own drive way). I just turned 20, but this started when I was 17. When I wash my families cars and do chores outside mainly on the weekends. I notice he looks at me smiling when I kneel down to pick up leaves he looks at me too. One time he was parked outside a different view of our house where the blinds were open. When my parents were not home, because I closed the other ones due to his truck and him being outside. Now he is here almost everyday of the week plus the weekends. It is strange because he doesn't live here it's his friends house he is supposively helping out with. He does clean, but its so little to be done and it looks the same. The fact that I am young and he smiles all the time is not appropriate since he is 45+ with gray hair and I am a young women just out of my teenager years. The guy who actually owns the property was very defensive when my mom talked to him about his friend cleaning up with his truck parked in front of our view and not even in the property drive way, plus they they have another parking place he doesn't use at the house which is on the property about 5 feet away. I have had an incident in the past as a kid.Any advice? Thanks