Am I doing the right thing?

This is a long story and situation. This all starts with my husband's "step nephew". Everyone including my husband has always said bad things about my husband's late step sister. She had his nephew when she was 14 years old. Everyone said she was fast and a whore and would sleep with older man. They told me the father of her son was unknown because she was always having sex with older men. When she got pregnant, my MIL kicked her out and sent her to live at a homeless shelter for teenagers.

My husband's nephew is 16 now and his mom died 8 years ago so my MIL took custody of him because his step sisters mother is on drugs and couldn't. He came to live with us two months ago because my MIL started dating a man who has been abusing him and he ran away. My husband tried to turn him away but I said regardless how he feels about his step sister, he's family. Blood or not and he's just a child. Me and my husband have 3 kids. Two daughters, one son, so I moved his nephew in with my son and things have been ok besides the nephew being a little messy and eating everything! He's a teen so I get he's hungry all the time. My husband's final straw was drawn Tuesday when my nephew ate my husband's birria tacos and he told his nephew he has to leave. He doesn't care where he goes but he has nowhere to go. The nephew was begging. I was trying to talk sense into my husband. There's no reason to send the kid back to an abusive home over tacos. My husband started pushing him out and his "nephew" called him dad and told him he's his only parent left. My husband made an expression that wasn't a wtf expression. But an oh shit expression. I asked my husband what he was talking about and my husband said nothing and the nephew was saying to stop lying. There was a lot of escalation but I found out the story.

My husband said he had been romantically involved with his step sister. Which if she got pregnant at 14 that means he was 19 or 20 when he got her pregnant. He said he never raped her but she tried to say he did. I've done my own investigating and contacted other her family and according to them he raped her. My MIL knew he got her pregnant and kicked her out. So he's had this child he's known about. Whether it was rape or statutory rape, he assaulted his underage step sister and then convinced me she was just a fast girl and bad mouthed her even after her death. And was gonna send someone he knew was his son back to a violent home. He left to give me space to swallow everything. I have let my nephew stay because he has nowhere to go. I'm speaking with a divorce lawyer tomorrow. But I'm wondering if that's the right thing to do. I haven't even told him I want a divorce. He thinks I'm just taking tim to think but this isn't something I think we can come back from