I agree that with more information it sounds like it is seriously crossing the line. You could probably just leave a recording app on your phone running whenever you are with him if you have space on your phone. If nothing happens you just delete the recording. His comments sound like they are moving from the area to sexual harassment and moving towards sexual assault. You can actually call the police if it has gotten severe enough and your mother doesn't believe you. Unfortunately the cops will require proof as well if it's just verbal still. You need to do something before it escalates further though, and even if he is a total pervert, confronting him over it (preferably with someone with you) might be all it takes to stop it.
Sexual assault can include:
•Any type of sexual contact with someone who cannot consent, such as someone who is underage, has an intellectual disability, or is passed out
•Rape
•Attempted rape
•Sexual coercion
•Sexual contact with a child
•Incest (sexual contact between family members)
•Fondling or unwanted touching above or under clothes
Sexual assault can also be verbal or visual. It is anything that forces a person to join in unwanted sexual contact or attention. Examples can include:4
•Voyeurism, or peeping (when someone watches private sexual acts without consent)
•Exhibitionism (when someone exposes himself or herself in public)
•Sexual harassment or threats
•Forcing someone to pose for sexual pictures
Any easy thing you can do for self defense that requires very little practice is, if wearing shoes with a decently hard sole, scrape the side of your foot down the attackers shin in a kicking motion. If you do it right it will stop most people in their tracks.