How to know if a relationship is moving too fast

Dear Jeff and Lori,

I'm struggling with letting my guard down in my current relationship. We were both recently separated from our spouses when we met, and he moved in with me very quickly during the first COVID lockdown. Both of our marriages were unhealthy, and I moved quickly to file for divorce. My partner, however, has a son who has been very open about his disapproval of his dad’s choice to leave the marriage. My partner says he is fully committed to me and has proposed, but is afraid that filing for divorce now will sever his relationship with his son. I also know that he’s in regular contact with his wife, and that she still wants to make the marriage work. I feel so insecure right now and keep asking him to finalize his divorce. Am I wrong to feel this way?

Signed, Insecurely In Love