Why did the boy let the girl touch him between his legs?

The specific situation you're referring to could vary widely in context and intention. It could involve a range of scenarios, from innocent play among children to more complex social dynamics in older relationships. It's important to consider factors like consent, age, and the nature of their relationship. If this situation raises concerns, it might be helpful to communicate openly about boundaries and respect for personal space, ensuring both individuals feel safe and comfortable. If you're looking for support regarding a particular situation, please provide more context.