I am hated by my ex-girlfriend, but I still want to get her back. Is it useful to send her a good night message every day?

Why waste energy when it's a foregone conclusion? If you have time to walk around her, you might as well make yourself happy. Don't dwell on it. The past is the past. There's really no point in watching these later. If you can't put it down, just put it down. The big deal is to find another woman and make you forget her. Emotional changes always happen. Or concentrate on work and life to enrich yourself, which is more practical.