I convinced my boyfriend to tell his mom TW

My boyfriend opened up to me that on his family vacation his cousins Liam and Abby had held him down and forced him to give Liam oral. At first he tried to say he was fine but before he opened up I notice strange things already. He didn't want to be touched. He was distant from me. He would tense up and breathe funny if I touched him from behind. My mom also lets him spend the night sometime and he had peed in my bed and mumbled "shit". He said it was a freak accident but he didn't seem that surprised he had an accident. When he told his mom I was there and she just looked blank. She told him it was wrong if them to do that but they're young like he is... Liam is 18.. Abby is 19.. My bf is 16. She said they're leaving for college next year so he won't be seeing them that often anymore anyway. He started to choke up and said she doesn't understand. It was bad and they told him to say "I love your cock in my mouth." He said fuck you and he threatened him and said "I will if you don't say it." So he said it.. His mom was very dismissive and just kept saying that they will be at college next year and started BEGGING him not to say anything. He started crying. And I held his hand. He said he was gonna spend the night at my house for a few days and his mom said ok... He cried a lot at my house and my mom talked to him because my mom has been raped. She also asked if peeing was a freak accident and he said no... So she bought plastic sheets to put over my bed since he's staying with us for a bit. I just want him to be ok. Some may think I'm too young for love, but I do love him and he didn't deserve this. It's terrible his mom is asking this way. I didn't know she was like that...