The main character found himself transported to an different reality - believe he moved back and forth several times. Definitely human(oid) in the other place. One thing I remember about the word choice differences is that the other reality referred to sex as "joking". Also seem to remember scenes in his den - either before or after travel. I think the woman from the other reality could come back through with him - and did on occasion.
Not much to go on I know - but I've read so many and this was soooo long ago.