I found out I was going to marry my brother!

Okay so I met this guy I never met my dad before we dated for months then he said he wanted to marry me His mom told him his was dead but wasn’t true. Then his mom came over the first time for a family dinner and acted strange when she saw my dad said she didn’t feel well and left home. Then my dad told me the truth that his mom didn’t tell him that she was pregnant by him when she moved states and never talked to him again what should I do my partner was really heart broken. I’m thinking of moving states to move on and he still is mad at his mom for lying to him about his dad and not telling him she was pregnant because my dad was still married with my mom and still is.