All the people telling her to get a new boyfriend.....like you have never looked at the history of your girlfriend/boyfriend......Its not like he stole her password and is reading her emails....just looking at the history.
As soon as you click on the address bar, the history can pop up, or as soon as you start typing, there it is! Relax people.
He is probably just seeing your search or browser history.
Depends what browser you are using, you can make it so that it clears the search and history every time you close the application (Dolphin HD gives you the option each time you close the internet).
Galaxy S SHW-M110S
Tegrak Kernel Build 38 - Rooted and OC'd to 1.2