Please help me with my boy

Hi, this is my boy marshmallow. He’s 4 years old. Since it is winter he lives in the garage instead of outside, so we bring him in for about an hour a day. Presently he has started to bite me and hump me as shown in the video. He has always been a very sweet bunny. I have no idea why he is doing this but I have torn skin, bruises, scratches, and tooth imprints all over my arms. He even drew blood today. Normally I push him off instantly but I decided to get a video and ask for help. I have 2 questions. Why is he doing this all of a sudden and how do I stop him? My sister is very young and he can't be doing that to her. Please help me get him to stop.