You need to go hunting with him for the 1st heart, go to the hot spring for the second, and for the third he needs to invite you over to his house iirc. You'll need to ask about his friend after finding the journal in the hut after starting the lost friend quest and ask about hunting to go hunting with him. You need to go on Friday between 18:00 and 0:00. To go to the hot spring you need at least 1 heart and ask about hot springs.