There you go. It's a slang term.

Technically it's a conjunction meaning "along with being" and is used hyphenetically (I don't think that's a word ). That or it's an abbreviation for cumulative.

The reference to having an orgasm or semen is merely slang. If your characters are speaking, they may use "cum". But it depends on your voice if you're using "come" or "cum" to refer to orgasm or semen (or the same for a woman's bodily fluids, i.e. "girl cum"). If your narrative voice is very informal, you might use the slang term, but if you have a more formal narrative, it's best to use more accepted grammar.