How common is it to marry the wrong person first, and then get it right with your second marriage? Are previously divorced people who still want children rare?

My partner has been married and divorced twice. He has two kids from his last marriage, he was happy to have another with me (or not, he said he wasnt opposed to it but it wasnt a dealbreaker for her if i didnt want to or couldnt, i really did want a kid though). We’ve been together seven years but arent going to get married.