In Chapter 2 after you get married, return to the valley to befriend the other two (now unavailable) bachelors. Give Gustafa flowers (any kind) and within two or three days he will be your friend. Give Rock flowers (toy flowers or mist moon flowers), any of the old coins from the dig site, or statues. Within three or four days he will be your friend. Give Marlin crops that you grew. He will take any of them, but will become your friend quicker with "A" crops or higher; also buy seeds from him and he will be your friend within three to five days.