if one can only feel regret. how his next life going to be. life is not something to be regretful. it's just something for you to try and if it does not turn out how you wanted to be. go find a roundabout and make a turn around and start over. life is too short to regretful. instead of being regretful you better fill it up with grateful.
footnote: a piece of lame advice yet useful for a friend :)