Adam Fisher was the husband of Susannah and the father of Conrad and Jeremiah. He's known to be a man who has to have his way no matter what it costs or who it hurts. He drives Conrad away after Conrad realized how badly he was treating Susannah such as regularly cheating on her, mistreating Jeremiah and abandoning the family when her cancer returned.
Despite all this, it is hinted and implied that he may have loved her, but failed to show it. He is shown to be an "asshat" and verbally mistreated Jeremiah while favoring Conrad as the two grew up. One example being when he yelled at him as a young child when he and Belly accidentially made a mess using his blender. He harshly scolds him, "Did I not tell you to not use the blender?" before Conrad reveals that he actually never did. This detail clearly stuns Adam and causes Laurel to reprimand him for his actions. Following Susannah's death in It's Not Summer Without You, he tries to sell the summer house. He tries to justify his actions by insisting the money made would go to his sons, when in reality he was just unable to have any reminders left of his late wife whom he mistreated. He is barely stopped in time by Laurel and Conrad, who get him to finally admit that he misses Susannah and can't bear to have so many reminders of her when she is truly gone. They convince him to simply give the house to them to look after as he tries to make peace in his life. He agrees on the condition that Conrad return to school and finish (and pass) his upcoming tests.
In the final book, We'll Always Have Summer, he has become a more friendly and gentle person than in the past. He tries to mend his rather broken relationships with his sons and family, making an effort to become a part of their lives again. He even pays for Jeremiah and Belly's wedding, despite not agreeing with them getting married at such a young age. He even shows great remorse for having drove Conrad away and vows not to make the same mistake with Jeremiah as he did with him.