A friend of a friend wouldn't marry the mother of his two kids because he "didn't agree with marriage". They broke up and he apparently is now happily married to someone else.
I know of a guy who got divorced after a long marriage and said he intended to live the rest of his life as a single man. He married again, eventually.
OP, because your man is going through a divorce it may just be a question of timing. But if you stay with him you need to accept it's likely you two will never marry, and to be at peace with that.
I haven't RTFT - apologies - but you don't say in your OP why exactly you want marriage, given that neither you nor he want more children. What is it you want from marriage?
I personally do not believe that marriage is something I need as a sign of someone's commitment. Someone's commitment is evident in the way they treat you and the level of love, trust and respect you share.
I know live-in couples who are devoted to each other and married people who carry on behind their spouse's back as though they're single. Marriage does not bring guarantees.
Unless you're marrying for children, money or to enable a foreign partner to live in the country legally, is it really necessary? Just call me an old romantic, eh! 