Husband cheated with my best friend

My husband and I have been married for 4 years. We have a three year old together. My best friend and her daughter came over to our home for NYE. We had a few drinks and toasted at midnight. Our son woke up so I put him back to sleep and went to bed. Everyone else stayed up drinking and playing games. New Year’s Day my best friend called me crying and saying that my husband came into the bed she was sleeping in and slept with her. She said she was blacked out and didn’t remember but her daughter had been in the room and was upset about it and told her. She said she told him “no” but then said she pulled her pants down for him. She is saying that she feels he assaulted her. My husband says he drank so much he blacked out and remembers nothing after midnight. I am lost and hurt. I have no idea what to believe or who to believe. I am getting ready to have surgery for possible cancer and I am so scared to be going through all this and be alone. Has anyone dealt with this before? I guess I am just hoping someone can say something to make me feel better.

Edited to add: I told her I would fully support her pressing charges and she said she doesn’t feel comfortable going forward with a police report at this time. I was confused about her daughter being in the room because when I woke up her daughter was sleeping on the sofa in the living room. Thank you so much for the responses and the different points of view. It is really helping me process this.

Update: l was told by the last person to see them that my friend was asleep on the sofa and my husband was in the kitchen. Her daughter was asleep in the other bedroom. At some point her daughter was moved to the couch and they moved to the bed (where there were no children) Nobody’s story makes any sense anymore. Unfortunately I don’t think I will ever know what happened. Thank you for all the kind and not so kind responses! ❤️ also a bit of context: my friend had slept with and had an affair with her other best friends long term live in boyfriend. She ended up marrying him then they divorced over infidelity issues. I just never thought she would ever do that again and not to me. Lesson learned. Happy New years everyone.