Silent one— I’m sorry you went through pain like that, I understand because I too have “lived through” a failed marriage.
Not only is hakaras hatov important, I feel its from the most important traits one can have for a happy and successful marriage.
Its all about being appreciated, where there appreciation things can be tough financially or otherwise and the marriage will continue to blossom, where there’s no appreciation people feel lonely and forgotton.
Now for seeing it in ur date,of course everyone is polite on dates however there’s a drastic difference between genuine and fake appreciation. Genuine appreciation won’t be a quick thank you for whatever you did that deserves appreciation, rather it will be lavish with words of appreciation. Cold thank you can be fake but if someones “thank you for……. I really appreciate it that’s genuine, and watch for the facial expression while saying it is there a smile? Its real. Also does the person feel comfortable saying showing appreciation or does it seem forced?