How do I prop-up or fix a wall that is slowly moving?
More than likely, the column of blocks has settled slightly causing your problem. I can't see from your picture, but has the gap between the top blocks and wall also opened slightly? If it has, then your blocks have shifted. Usually the weight of a large gate, such as you have, causes this problem on a fairly new install, especially since you only have a one block column.

My suggestion would be to add some "L" bracket supports or other mounting directly to the wall and column. Use your imagination and I'm sure you can find or make something that would look nice with the finish of the wall and blocks. Whatever you use, be sure to mount it to the block first, flush to the finished edge. Then screw or lag it into a good solid point of the wall (stud or plate) in order to use the mechanical advantage to pull the column, close the gap and restore the column to the original plumb-line, or at least stop any additional settling and tilting. Mounting the brackets to the same block the gate hinges are mounted to would help support the weight of the gate and not stress the mortar joints of the rest of the column. Be sure to consider sealing any devices you may have to install in the wall to prevent any water from entering. If you end up needing to use some ugly but strong utility type brackets, you could build a nice looking small valance box covering and stucco it to match.  Lots of decorating alternatives.

The bottom line is to devise a way to attach the sides or top of the column firmly to the building and stop the settling from getting worse and making your nice gate inoperative.