How can the love of one's father be developed in the heart, especially with his numerous demands, and in light of his ill temper and quick exasperation due to asthma?

You must be dutiful and kind to your father, for dutifulness to one's parent is one of the greatest means of attaining Allah's pleasure and earning reward in this world and the hereafter. The more you fulfill his permissible wishes, the greater your dutifulness to him will be. As for heartfelt love, you are not sinful for lacking it, but sound human nature dictates loving one's father. What will help you be dutiful to him and gain his love is remembering his kindness andفضل (favor) towards you, and thanking Allah for this blessing, for whoever does not thank people does not thank Allah. And know that no matter how hard you strive to be dutiful to him, you will not fully repay him his right, as the Prophet, peace and blessings be upon him, said: "No child can repay his father unless he finds him enslaved and buys him and sets him free." You should recall the many texts about the virtue of being dutiful and kind to parents, and that pleasing them is one of the greatest means of attaining Allah Almighty's pleasure. Seize the opportunity of your father's life to draw closer to Allah by being dutiful to him, and seek Allah's help through supplication and striving to fulfill his right.