I don't think that you being aroused by a woman makes her your future wife. In fact, your arousal doesn't necessarily mean that you desire her. I read an article from TED Blogs that someone posted here just yesterday that desire doesn't come before arousal; it's, in fact, the other way around. You can be physically aroused by someone, yet not want them.

Erections are nothing to be ashamed about. They happen to men all the time. It simply shows that your body is functioning in the way it should.

If you want my opinion, I think you should just relax and take things one day at a time with your lady friend.