What if you did his part in third person and don't show everything he thinks? Might that help? Make it more distant than the other POV.
Even without what he thinks...he would be hearing and seeing things that I haven't revealed in her POV. It's inevitable. She doesn't have a clue about her past...he's a part of her past, in a way.
I guess if I wait to throw him in until after she's had more revelation, it could work. It'll be tricky...but I do like the idea of it.