Would you believe your son or your husband if your son lies a lot

My 14 year old told me some disturbing things about my husband, his own dad. He said this happened over a month ago and he really didn't know who to tell because if he told his best friend he wouldn't be allowed to come over anymore. This is disturbing but he said he caught his dad in his room with his best friend's bag smelling his underwear. I was extremely disturbed. He said his dad promised it wasn't weird and made him promise not to tell but it's been stressing him out. I immediately confronted my husband and my son started panicking because he apparently promised not to tell. My husband denied this and asked why would I believe anything our kid says when he has been lying so much. He started skipping class this year a lied about it and also lied about his report card and forged our signature. We also had a problem on Halloween where he lied to us about him and his friend having a sleepover and they actually went to a Halloween party. My husband is saying I'm gonna ruin his life if I say anything and that I need to not believe anything our son says because he's shown time and time again that he's not trustworthy. Today my husband has mentioned taking our son out of school and homeschooling him as punishment and he can't have friends anymore. That way he doesn't ruin his reputation. This is really confusing. That's such a disturbing lie and idk how to feel or who to believe. I know they say always believe your child but my son isn't saying this is something his dad did to him. He did it to his friends underwear and doesn't seem like the friend even knew if what my son is saying is true