Single people often wish they were married because single people are lonely and want companionship. They think there are no down sides to not being alone or think the advantages outweigh the disadvantages. (With the right person, that is true- not too many RIGHT PEOPLE though).
Married people often wish they would get a break from the other. When you wake up, she’s there. When you come home, she’s there. When you go to sleep, she’s there. (Same for “he”.) All the good things are there but all the bad things that irritate you are too. Because none of us are identical there will always be irritation and compromise and putting up with the others’ crap. YOu just have to try to find someone that has minimal crap to put up with and a lot of good stuff you both are good with.