How to prove that a former spouse is cohabitating with a lover?

To prove that a former spouse is cohabitating with a lover, you may need to gather evidence such as witnessing them living together, photos or videos showing shared living arrangements, mail or bills addressed to both individuals at the same address, or testimonies from neighbors or acquaintances who have knowledge of their living situation. Consulting with a lawyer to understand the specific requirements in your jurisdiction can also be helpful.