Preface: I'm new! lol

I've been watching tutorials and made a simple shirt from a male model by copying the model object and removing everything except the shirt area and then scaled it. easy.

However when I select the shirt in edit mode..Deform...smooth vertex it breaks apart or tares at the seems? Also when I set it as a cloth and animate the shirt against the male model as the collision point it also tares at the seams?

Q... How do I set my shirt so it stays together?