Not even dating, haven't ever dated

So I honestly feel like my SO doesn't love me. I feel as though he's only with me because he thinks no one else wants him. I ended things with him after 7 months because I felt like a fuck buddy. He cries and cried, he was so broken. He said he was depressed without me, and needed me in his life. Or he said. After a couple months I agreed to try again and he's changed, kinda. He hardly ever talks to me, and even though he works, he will get out at noon and I still hear nothing from him. He will also bring up the fact that after I ended things I dated another guy. I feel like he's putting 0 effort in and I think I should give him a taste of his medicine.

FYI this man says he wants to marry me