Amanda, you start by having a conversation with him when you are both sober. At this point in time, it would appear that you've not told him that you don't want to be just a casual girl to him. Tell him that you don't want to be friends with beneifts. Tell him that you only want to have sex in a relationship. If he's not interested in a relationship with you, then he's not the man for you.
After having this conversation, try staying sober for a few parties. All these scenarios are happening when you're too drunk to stop him or have a conversation with him - and you need to be responsible for your own part in this mess.
As for him, do you realise that he's taking advantage when you're too drunk to consent properly? What he's doing to you is called sexual assault.
Never regret anything that has happened in your life. It cannot be changed, forgotten or undone. So, take it as a lesson learned and move on.