You state that you think the man in reference has feeling for you, why then did he not get engaged to you?
Nevertheless, if he gets married, he can still marry you and you can be his second wife. Would you be content with this? Would the first wife be content with this? If you are happy and content, then apart from making Du’aa, you may adopt means and propose to the man to get married to her. You may measure your thinking of his love for you through his response.
and Allah Ta’ala Knows Best
Mufti Ebrahim Desai