Practice Extreme Honesty
Chances are, you're not the only one who is sexually frustrated; She's likely experiencing the same temptations you are. By talking about the difficulties you're facing, rather than hiding them, you can become a lot closer, and learn things about one another that would have probably never been discovered otherwise.
Try practicing extreme honesty. Tell her about that girl at work who keeps hounding you to grab a drink. Explain the things that are giving you trouble and the aspects of your LDR you find most difficult. She's likely experiencing similar struggles, and by openly admitting what your stumbling blocks are, you can mutually work towards a solution.
By keeping communication open, you're also building trust. And the more honest you are with one another, the less you'll have to worry about what you're up to when you're apart.