Therapy won't make you happy.
There are more fulfilling and interesting states than simple happiness. Therapy won't stop you being bereaved, won't stop the people you love suffering, won't delete past trauma, won't mean work is always perfect, won't stop the kids leaving home one day, won't mean you are never left by a lover. It will mean that you are able to accept these things, that they won't feel confusing, that you will have an inner peace and stability that will see you through difficulties, allow you to mourn sadness without disintegrating and will allow you to enjoy the life you do have instead of longing always for another.
If a child says; 'I'm hungry' and meets the reply 'No, you're not! You've just had lunch,' that child might grow up into someone who really doesn't know whether or not they are hungry. Having your actual experiences flatly denied makes us unable to be sure of our own perceptions both about the world and about our bodies. The doubt can extend to everything - I don't know if I like my job, my partner, this food, sex, this place, this house. In therapy I've find that most people actually do have an idea, but it is kept very secret. Allowing ourselves to name our own experiences and keep them, even in the face of others experiencing the same thing very differently (or claiming to) is difficult, but possible as long as we can take our inner world seriously.