Many readers and writers are opposed to the use of the word ‘cum’ as a verb and it is a hotly debated subject. For me it is perfect for describing both the ejaculate and the act of ejaculation, although this is not strictly the correct usage.
The word ‘cumming’ precisely conveys my meaning to the reader without any ambiguity. Just the sight of the word fills me with deliciously naughty thoughts. ‘Coming’ does nothing for me - I use it only in my romance novels or when I have to submit a piece of ‘literary’ work.
While the debate rages on about the proper to use of the word, and since I have never been proper, I will ‘cum’ as and when I please!