^^
Trust has to be earned, just as privacy and boundaries should be respected.

OP; I am a secretive person. I always have been. I only share certain information when need be, and I enjoy my time alone. And there is nothing wrong with that. If your partner is getting suspicious, I would just explain to him that this is part of who you are, and it's not a part you're really wanting to change.

I honestly see no problem with privacy in a relationship. It is when a suspicious partner starts over thinking that problems start. Some of us need more time alone than others, that is just a fact of human nature. And it's alright.