Hezaa, I would avoid trying to have any deep or extended conversation with him on your last day. You know you would be speaking from a place of insecurity and risk pushing him further away. You said he doesn't like to talk about your "feelings or psychology stuff" so I would advise you not to go there on your last day. If you wrote a letter is there someone who could read it for you and help you strain out anything that comes off as clingy or needy? That way you could voice your regret and appreciation without making him uncomfortable and still feel like you did what you could. I know it's hard, but you have to try not to act out of desperation to keep the relationship.