What were Thales's views on marriage and sexuality?
Allegedly, when someone asked him why he didn't have children, he replied "Because I am fond of children."
The source of stories about Thales, marriage, children and sexuality is mainly Diogenes Laertius, Lives and Opinions of Eminent Philosophers, given extra circulation in Plutarch's Lives.
Given, then, the unlikelihood that Plutarch had access to any genuine work of Thales, what were his sources for this Milesian? Only twice are these specifically mentioned. One is at Vit. Sol.[Vitae Solonis, Life of Solon] 6, 1 ff. where Solon visiting Thales at Miletus, was astonished at his host's indifference to marriage and the begetting of children (cf. Quaest. conviv. 654 D and Diog. Laert. I, 26). After tricking Solon into believing that his son is dead, Thales explains that though the report is not true, such uncertainities prevented him from marriage and raising a family: these are the things Hermippus says Pataecus narrated ... Plutarch used Hermippus of Smyrna elsewhere in the 'Lives', there is no doubt the story comes from the Peripatetic biographer. (Jackson P. Hershbell, 'Plutarch and the Milesian Philosophers', Hermes, 114. Bd., H. 2 (2nd Qtr., 1986), pp. 178-9.)
Diogenes Laertius on Solon can be checked at :
Very little credibility can be attached to the relevant sayings and anecdotes, for which there is no external confirmation.
Jackson P. Hershbell, 'Plutarch and the Milesian Philosophers', Hermes, 114. Bd., H. 2 (2nd Qtr., 1986), pp. 172-185.