Bellatrix and Rodolphus had been married 9 years, they were married when Bellatrix 21 and Rodolphus was 23. They would have been married 4 years earlier but the Dark Lord had forbidden it, he was interested in Bellatrix and wanted to train her.
Their marriage served no other purpose than to produce pure blooded children, but none had been born. As much as Bellatrix despised the idea of being a mother she knew it was her duty. The Dark Lord had told her once that it was a pure blood witch's duty to give birth to pure blood children. But she hated her husband, they shared a bed every night but he only touched her once a week.
It was not a matter of unrequited love on Rodolphus' side; he hated Bellatrix as much, perhaps as even more that she hated him. He had married her on his father's orders and the Dark Lord's. Bellatrix had told him on their wedding night that she had never experienced love. But as soon as Rodolphus had introduced her to the Dark Lord she had fallen deeply in love with the Dark Lord and became loyal and obsessed.
Bellatrix found out she was pregnant when she was 30. She had shown no emotion when she told Rodolphus. The Dark Lord had read her mind and been furious with her but he soon forgave her as long as she didn't stop serving him to look after the "Brat" Bellatrix had promised she wouldn't and her eyes had brimmed with tears when he told her he wished her well.
She had tortured the Longbottoms while their son cried even though she was 2 months pregnant. When she was imprisoned in Azkaban she was 4 months pregnant and had lost the baby with great relief in her cell. The baby fitted into her hand. She threw it out her barred window and the body fell into the rough sea.