Commander Lawrence and Serena/Naomi

I’m on episode 8 season 5. I just watched the episode where Commander Lawrence asks Mrs Putnam to be his wife purely out of convenience since Commander Putnam was executed for raping Esther. We know a widow with a child cannot be single and Lawrence needs to follow Gilead’s values to gain more power so the proposal works for both of them. Earlier in the season Serena insinuated the same proposal to Lawrence and all he said was “Do you expect something out of me Serena?”

This makes me wonder how come Lawrence didn’t ask Serena to be his wife?