Coaches ask questions to help one or both partners in a relationship to improve something – for example, improving communication, personal growth or helping them respond to needs better.
Improvement will be judged on metrics decided on by the stakeholders. Therapy is more about providing a safe space for people to communicate so they can resolve emotional issues or so that they can come to terms with something that is hard to talk about (e.g. a previous divorce, infidelity, illness or a death, etc.) or pathologies that are preventing someone from being happy.
Essentially, therapy clients are looking to heal; coaching clients are looking to get results (according to whatever goals they set); therapy clients want to understand why they feel what they feel; coaching clients want to take action to change their lives.