Answer: Geraniums do best with full sun (a little afternoon shade in really hot summer areas), a little less than average watering, and minimal fertilizing. You were correct to remove the spent flowers -- pruning them off was not the cause of the problems.
It's possible you are "killing it with kindness." With too much water and/or too much fertilizing, geraniums quickly succumb to root and stem rots. Once they become infected, there is little you can do to stop the infection (including repotting in clean soil since the infection is in the plant's system).
I suggest giving the plant as much sun as possible, holding back on the water significantly (but not to the point of desert conditions), and cutting off any soft, mushy, brown-to-yellowish stems (dip your pruning shears in a 10 percent bleach solution between each cut). Hopefully, it's not too late.
Q&A Library Searching Tips