Разница

  • В чем разница?
    I want him to come back
    I want him back

  • В значении разницы нет.
    Просто во втором предложении пропущен инфинитив to come.
    В разговорной речи это допускается.
    Сравните: I want him here. He proved ( to be) a talented musician. The work done (When the work is done), I want you to join me.
    Обратите внимание: речь идет о двух инфинитивных оборотах, а также о независимом причастном обороте.

  • "We very much regret this decision, which risks having regional and global repercussions.
    We also regret the order today to deploy Russian troops into eastern Ukraine, reportedly on a “peacekeeping mission," says United Nations Under-Secretary-General for peacebuilding Rosemary DiCarlo

    почему в речи не был употреблен предлог about?
    "about this decision" - Мы очень сожалеем о данном решении...
    "We also regret about the order" - Мы также сожалеем о сегодняшнем указе...

  • Потому что это не русский язык.
    regret
    verb
    US /rɪˈɡret/
    -tt-

    to feel sorry or unhappy about something you did or were unable to do:
    [ T ] He regretted his decision to leave school.
    [ + (that) clause ] I regret (that) I didn’t buy more when they were on sale.
    [ T ] I’m going to regret eating all those nachos.