Is this sexual assault???

So this happened a little over a week ago but I have been to embarrassed to post about it. So my cousin and I decided to sleep in the same room at my grandparents house on Saturday night two weekends ago. He slept on the bed and I slept on the floor. It was about midnight and he asked me to switch spots with him cuz he is like 6 foot and the bed in there was way to short for him. I switched spots with him and tried to fall asleep. By the time it was 1 o'clock I was REALLY close to falling asleep and my cousin asked me something. At that point I was so close to falling asleep that I didn't even hear what he asked and groaned in approval. After I approved, he moved up on the bed next to me. I had already approved...by accident and was to tired to tell him to get off. I moved as far over to the wall as I could because I was uncomfortable with him being on the bed with me. I was laying on my back and he was laying on his side facing me. He was slowly inching closer to me for about 20 minutes until his hand was lightly touching my side. At this point I was SUPER uncomfortable! I turned on my side facing the wall and moved as close to it as I possibly could. He kept inching closer and eventually I felt something on my lower back/upper but region. It was his dick...hard. I kept trying to move further and further against the wall but he kept inching closer. I was extremely uncomfortable and disgusted so I quickly got up and moved to the floor.

Is this sexual assault?