Okay kiddo, so a lavender marriage is when two people who are actually gay or lesbian get married to someone of the opposite gender. They do this either because they want to hide their real feelings or because it's more socially acceptable to be in a straight marriage.
It's kind of like pretending to be someone you're not. Just like playing dress-up and pretending to be a doctor or a firefighter, except in this case, they're pretending to be straight.
Unfortunately, when people are not true to themselves, it can cause a lot of stress and sadness in their lives. It's important to be honest and true to yourself, even if it's hard or not what other people expect.