R.M.
My thought is that your boyfriend needs to respect your wishes. I don't have PTSD, but I wouldn't like someone grappling me while I was sleeping either.
You say it's been getting worse lately, so I think you need to sit him down, and tell him strongly that you do NOT want him grabbing you in your sleep any more.
If his grabbing you is his idea of a precursor to sex, then you need to discuss with him ways he CAN seek intimacy without humping you in your sleep.
PTSD or not, you are entitled to set whatever boundaries are comfortable to you, and your significant other must listen to you and abide by them.