How can I fix this, ?

Hello Millie, You need new sheetrock to do this right. For the best outcome call a carpenter to do this job. Unless you know just what your doing, call a professional.

Hi Millie. Have your roof checked and if the pipes are in the attic, have those checked too and the a/c spill pan. No matter how humid it is, this shouldn't happen. Good luck.

Check out the real cause of why this happens. You could put up mouldings to cover it while the wall beneath will still move. You could use a good quality caulk to fill the cracks first and then apply the mouldings.

Not sure where in TX you are but it is far more common than you might think. The underlying problem is most likely your foundation. The ground shifts with the drying & rehydration of the earth under your foundation which allows foundation to shift. When founations shift, so do walls & hence inside wall joints separate, peel, & caulk & mouldings come loose, & even including roof valleys ,flashing & shingles which also allow water leaks both major & minor.

To fix, you need to have your foundation re-leveled before making any repairs, otherwise, this will keep happening.

Should you have a concrete slab foundation, you still need to have it checked. Cracked drywall or joints showing up uneven around doors or Windows or doors or Windows not closing properly may indicate foundation issues even with a concrete slab that will crack under floor coverings.

I would encourage you to fix foundation level rather than trying to just keep covering it up. Pier & beam foundations do require leveling in Texas from time to time more often but concrete slabs are not immune to it. Nature of TX soil.

it also looks like water marks too....any roof leaks or pipe issues?

Use a Crown Moulding to cover this .