Returning to Buddhism -Sex is not forbidden in Islam. But reserved in lack of better word, to married people.
Because in Islam everything happens professionally. So marriage requires contract as much as business does. Marriage is a type business technically.
Although; i think this is not a metal excersice. Write contract, do it. Follow The Law.
If anyone does not take my rights by force or not, i can not complain about him. I will speak about rights although right is a Political term. But i will stop here.
While there are specific Buddhist groups with specific local rules, Buddha himself didn't teach much about marriage. Buddha (according to the story) was married and had a son, Rahula (some of the Sutra - believed to be the Buddha's own words - are addressed to Rahula).
Generally, because Buddhists believe that all sentient beings are in different places on different paths, learning different things while heading toward enlightenment, many Buddhists consider things like "a good marriage" a personal thing, and that one person's personal thing shouldn't be forced on others - it would cause them distress.