My spouse has a long illness and I am exhausted from caring for them. How can I keep my patience and good conduct?

Caring for a sick spouse is among the deeds with the greatest reward, but the carer needs care too.
In a hadith qudsi narrated by Muslim, Allah asks on the Day of Judgement why His servant did not visit Him when He was ill — meaning that whoever cares for the sick finds Allah with them (Sahih Muslim, Kitab al-Birr wa as-Silah wa al-Adab). ʿUthman ibn ʿAffan r.a. stayed away from Badr to nurse his sick wife Ruqayyah, and the Prophet ﷺ gave him a share of the reward. Yet carer exhaustion is real. Share the tasks with siblings and children, ask neighbours or the mosque for help, take regular breaks, and do not be ashamed to seek welfare support or counselling. Losing your temper now and then from fatigue does not make you a bad person; apologise and carry on. See Mental health and Zakat & welfare assistance.