Sodapop never planned on getting married after Sandy left him. He still wanted to marry her, he still loved her after all.

But,

He was so depressed, and miserable. And bills were piling up. Darry mentioned an arranged marriage for himself so they could afford to live but, Soda didn't want Darry to get married. He knew Darry didn't want to yet, and Ponyboy is too young. So,

Sodapop decided to go with the arranged marriage.

Darry was hesitant, not wanting his younger brother to do this but, Soda argued. If he couldn't marry Sandy, he'd just do an arranged marriage so at least then he could be some help.