With adults, I might agree with GreySage's sort of advice, but given your ages, I strongly suggest you immediately kick this player from the group, do not let him into your house next session, avoid being anywhere near him without an adult nearby, and get the help of parents to, well, basically enforce these things. Talk to your parents, who I really hope you can go to for support with this kind of problem, and ask if one of them can be home the next day you play (it's possible they can take a vacation or sick day, or even change their schedule a bit, depending on jobs/companies). Failing that, literally anyone older who you would trust with your life, basically? An older (17+) sibling or cousin, a close adult relative, or even if there's a family friend who you would trust to have your best interests in mind in this situation (though, with family friends, it may be best to run that particular option by your parents. Uncle Harry, your hypothetical dad's lifelong friend who's not actually related, might be a great guy to your knowledge, but your dad will know how he'll act in this situation).
Once you and your other players are safe, and no longer experiencing this player's, well, behavior issues, then, if you want to try to help him, you can do that. If you want to try to talk to him, that might be a good idea, and maybe what he needs, but it should be with an adult in the house, if not room. I get that maybe he won't want to talk about whatever's going on in his life if there's an adult in the same room, I remember enough about being a young teen. But... he's evidenced that he's not entirely safe to be around, especially alone. So if you try this, have a trusted, significantly older person available to intervene, should it be necessary. Maybe after a discussion, if he renders a genuine apology to both the group, and the young woman he assaulted, then the group can discuss among themselves, without him present, and if everyone agrees to give him another chance, and the young woman's opinion basically counts double here, then you can give him another chance, with an adult in the house, until you and the group, and the adult agree that whatever was going on to drive him to that behavior is mostly handled. In this course, maybe have a one-on-one discussion between you and him (with adult near, but only intervening if necessary) and then another between the group as a whole, again, with an adult near. Though... this can raise further difficulties, because, well, honestly, if I've learned anything in my 34 years, it's that communication is really goddamned hard. All the more so in situations like this.
Another option you might consider if you want to try to help him, is talking to a trusted teacher or school counselor who knows this person, because they will have additional avenues they can pursue to try to get him whatever help he needs (and honestly, that probably includes therapy, but to be honest, probably around 90% of people need some therapy, so, it's not really slight against him there).
But, "put your own oxygen mask on first before helping others." Your safety is paramount. Make sure you, and the other people being affected by this person's behavior are safe first, then you can see if you can help him. But your safety, and comfort have to come first.