Most Helpful Guys
Never do anything you are not comfortable with when it comes to sex. Tell him what would be acceptable to you and what isn't and tell him if he doesn't respect that you will break up with him. I know it's not easy to do it, but you need to.
The verbal declining should already be definitive, but his continued acts of coercion are already blatant disregard/disrespect of you/your will as an equal partner/human being. That should be a red flag.
He's being abusive? Check your jurisdiction's laws on molestation, sexual assault, rape, etc. and warn him accordingly against further criminal acts. If he's doing this out of ignorance, it may save you, him, and any other girls he encounters in the future from the unnecessary trouble. If he continues to do so nonetheless, rebuke him via text/e-mail/social-media private-message, so (if he admits to/fails to deny the charges) you have documented proof of the criminal acts. If he still does so, dump him and report him.
Most Helpful Girl
If he is abusive. You shouldn't be with him. Tell him that you don't want sex with him. If he doesn't take no for an answear, you should tell your parents about it