Londo Mollari had 3 wives. It was as though he kept a harem. Granted that he didn't seem to love his wives, he still had his sexual needs and he should still sleep with them occasionally. An accidental "by-product" is likely to happen. Besides, Londo was a great romantic. In one of the episodes in Season 1, he had a touching romance with a dancer who betrayed him. Yet, Londo sought to protect the dancer. Furthermore, he later became Emperor. As Emperor, there will be plenty of opportunities to make love with women of his choice in his kingdom. Even more so as Emperor, he had a duty to the Empire to produce an heir to succeed him even if he is gay which he obviously was not.
Why doesn't Londo have any children? This seems like a great mystery to me.