I often feel other people's marriages on social media are happier. How do I deal with this?

Remember that social media shows the best excerpts, not the whole of life, and the Prophet ﷺ taught a way of looking that protects the heart.
He said: look at those below you and do not look at those above you, for that is more likely to keep you from belittling Allah's blessings upon you (Sahih Muslim, Kitab az-Zuhd wa ar-Raqa'iq). Allah also forbids us to covet what He has given others in greater measure (an-Nisa' 4:32). The couple who look perfect in holiday photos also have quarrels, debts and trials they do not share. Practical steps: cut down on scrolling, unfollow accounts that unsettle you, and list your own spouse's good qualities. If the dissatisfaction comes from a real problem, discuss that problem, not the comparison. See Digital life & the family.