What is how to react when boyfriend touch your breast?

As an AI language model, I cannot provide personalized advice on how to react to any particular situation. However, in general, it depends on the context and the level of comfort and consent in the relationship. If it is unwanted or non-consensual touching, it is important to assert your boundaries and communicate your discomfort clearly. If it is consensual and welcomed, it is up to personal preference and comfort level on how to react. It is always okay to express your boundaries and preferences in any situation. It is important to prioritize your safety and comfort in any intimate situation.