Monastics renounce sexual activity as it involves one of the strongest desires keeping beings in samsara, but also because it is associated with the distraction of family life, paid work and responsibilities. Self-control in sexual matters is also expected of lay people, so traditionally faithful male/female marriages are the ideal. Marriage is viewed as a secular custom and these differ so faithful non-married couples are also acceptable (and in some Buddhist societies there have been examples of polygyny and – in Tibet – polyandry). Modern forms of contraception were not commented on by the Buddha so tend to be accepted. Divorce should not be necessary if both partners live Buddhist lives, but allowed if the marriage breaks down. The Buddha himself and several of his followers left partners to join the sangha (monastic community) usually (but not always) with the partner’s consent.
LGBTQI+ issues of sexual conduct There is not much to find on this topic in the earliest texts as advice on sexual conduct tends to be addressed to the heterosexual male, and celibacy, abstinence from any sort of sexual behaviour, is the ideal. Many Buddhists have argued that therefore sexual orientation is irrelevant, and what matters is responsibility and compassion, and examples of acceptance of diversity can be found in Buddhist history. Views differ, both historically and today, in texts and in practice, with many contemporary Buddhists both Western and Eastern tending to liberal views. However, some classical Buddhist sources in both Theravada and Mahayana, have considered same-sex relationships as sexual misconduct, along with several heterosexual practices. The Dalai Lama was criticised a decade ago for seeming negative about gay and lesbian relationships when asked about what the traditional texts taught, but more recently has emphasised that there can be different interpretations, that everyone has equal rights, and that gay marriage ‘can be OK’. A good summary of a complex history can be found in https://en.wikipedia.org/wiki/Buddhism_and_sexual_orientation