I think the issue has been well addressed already. As has been said, your description most certainly does not constitute rape. Whether there is sufficient evidence to support sexual assault is difficult to say. However, one important point to remember:
"I just want to figure out what I can charge him with"
You cannot charge him with anything. The Crown Prosecution Service (CPS) figures that out and lays charges where appropriate.
"It's up to your girlfriend to press charges."
No it's not. As above the CPS decides whether or not to launch a prosecution and they will do this with or (if they can and must) without the co-operation of the alleged victim.
"...im just want to figure out what law it is "
She should take her concerns to the police and let them, along with the CPS, do the figuring.
"Im not going to take him to court "
Sorry to labour the point but it has now been mentioned a few times. "Taking him to court" (whether you intend to or not) is not within your gift. Your "law enforcement class" should have taught you that in the UK charging decisions are made by the CPS and no other person (including the victim) has the option.