I have a small dialog where a user can add an email to subscribe.
I am torn between changing the subscribe button to take 50% of the place and adding cancel or simply make the
Any other suggestions?
I would recommend going with the cancel option since most users might not be used to the concept of using the close icon (the X) to close a dialog in a mobile app (you have them in websites) but then with a mobile app the common affordance to what I have found is to to have a distinct cancel option as shown below:
For the most part I would go with a dedicated 'Cancel' labelled button rather than an 'x' on mobile.
The target area is generally to small for the user to have a fluid interaction. If you make the 'x' a bigger target area it can be used. A good size might be the one used for delete options(red -). It seems to work quite well for apple so far.
Not exactly related to your scenario, but a general trend in iOS search/input fields. Put a small cancel button near the input field.