Dwarf Azalea

Question

What is the cause of my Azalea to collapse open in the middle

Answer 1

First, make sure you are giving your azalea the proper conditions for it to stay healthy. Making sure it is in well-drained soil and doesn't get overwatered is especially important, but azaleas can also be killed by drought.
https://www.gardeningknowhow.com/ornamental/shrubs/azalea/azaleas-noteworthy-shrubs-for-any-garden.htm

Or, your azalea might have one of the diseases or problems listed here:
https://www.gardeningknowhow.com/ornamental/shrubs/azalea/common-azalea-problems.htm