If seriously asking, there was a timeskip. Short hair is the FMC (original gf who he cheated on) from the first part (until 72). Seems like she didn't end up with MC even with how 72 ended (she said she is single now). Other woman is a rando AV actress we just got to know.
For now it seems like the author is gonna pull a reverse UNO and after the breakup force changed her randomly into brainmush stupid to have her act in AV/porn which will then be seen by MC. Probably the weakest way to get back at him, meh. Think some other "ha! in your face!" would've had infinitely more impact than changing her randomly and having her do porn. Sadly reads like the most generic writing ever.