For the first 50 years of his life, no one worried much about Roland's, Delain's crown prince's, lack of an heir. It didn't really seem pertinent, and things in the kingdom were good, so there was nothing to worry about.
Sure, there were some rumors within the kingdom as to the cause for the lack of an heir. Some assumed Roland was incapable of producing one, some assumed a love child would be brought fourth if necessary. Some wondered about the lack of women who were connected to Roland, but those thoughts were quickly dismissed. Roland is a very capable and virile man, he must not have wanted to settle down with any of them. Some wondered whether Roland leaned into another direction, wondering if his many hunting trips had ulterior motives. There were still some, those who had chosen a solitary existence through religion or profession, who wondered if Roland was like them, someone who had no interest in the pleasures of the flesh with other people. No one ever brought up the last two rumors except in barely audible whispers within just the right company. But while the Queen was alive, the kingdom was safe, whatever Roland's proclivities were or weren't.
But when his mother, Lita the Dowager Queen, died, even through his grief, Roland knew that despite his disinterest and worry about women, he would have to give the kingdom its next ruler. He was already 50 years old, and his time was running out. He didn't trust Randall Flagg much, but knew that he would have to rely on him to help with find himself a wife, and help him follow through with the unpleasant act that put babies in women's bellies. Roland knew that Flagg's knowledge of his lack of interest wasn't a good thing, that it was one more thing the wizard held over him, but it was no use. Roland was the way he was, and he needed help to fulfill his duties.
Flagg brought him women from the edges of the kingdom, and Roland chose Sasha, a young girl who was the least intimidating, and was the least likely to be bothered by Roland's inexperience and fear in the bedroom. On his wedding night, he drank the disgusting potion that Flagg made for him, and through his connection to Sasha, he managed to perform somewhat.
And through the years of their marriage, Sasha and Roland truly fell in love with each other. Their love weathered separate bedrooms and Roland's rare visits to Sasha's bed. Roland felt bad for not performing neither his husbandly duties as much as he was sure Sasha wanted him to, because Sasha was not like him and enjoyed the act that was supposed to produce the kingdom its next king. He also felt bad that they hadn't managed to fulfill that duty either, because Roland was certain that Sasha would make an excellent mother to a future king.
It took many years of trying but after four years of marriage, after the one night Roland and Sasha spend together in her bed without Flagg having to make him a potion, Peter was born. He was so much like his mother, and Roland loved him dearly. He was glad he had at least given Sasha a son and the kingdom an heir.
Sasha was more than the mother of a future king, and while they continued to be infrequent, Roland didn't stop visiting her room every few months. The last time they shared a bed was an ugly occasion that neither one of them wanted to talk about afterwards. But that night produced Thomas, and something good might have come from it, if Sasha hadn't perished in childbirth.
Roland mourns the tragedy, though he loves his sons. He never thinks about remarrying, and no one brings it up. Roland and the whole kingdom loved Sasha too much. Peter is growing up into a great man who will make a fine king someday. And though Thomas is too much like Roland in some ways, he is also a good son.
If Roland had been left to his own devices, he wouldn't have sought a marriage and children. But he was also raised with the knowledge that he'd be a king some day, and he knew he didn't have the luxury of choice when in came to certain things. But while he wouldn't have chosen to have a wife and children, he ended up being lucky. He loved his wife, and he loves his sons, though in slightly different ways. While having children and a family was his duty as a king, it did end up making him mostly happy.