Getting engaged to someone else while still legally married 🤔

I want to clear the air first before everyone is quick to judge....I'm NOT engaged to him. He wants us to just quickly get on with our life and be together and tell people we are dating, move in together and propose to me. I'm extremely hesitant because my gut is telling me that its not right until his divorce is finalized. There is still some wrinkles that need to be ironed out but he's been separated from her for nearly 4 years now. He started the divorce last year because he knew i was the person he wanted to be with and wanted to marry me. Before me he didn't care to file papers.

Am I wrong to feel this way? Not wanting to be engaged to a married man? Or am I just overreacting like it shouldn't be a big deal?