... The restriction of 1st person works for some things, ...
... I wanted ot keep the thoughts of the female character from the audience at this time.
The purpose being a touch of suspense. ...
These two comments are ones with which I agree entirely. First person is, if you think about it, ideal for whodunit stories where the reader only sees, hears and knows what the detective can (red herrings and all). There it makes perfect sense.
In erotica, particularly the darker elements, where there is a level of domination involved, then the reader generally needs to know what both parties are thinking in order to appreciate the full excitement of the situation.