Don't let it come into your thoughts, it's a form of infidelity to entertain advances like that.
Become a little withdrawn at the thought that if someone is flirting with you like this, then it probably happens to your partner a lot too.
Strike up a conversation because you think you might be able to just be friends at the very least.
Secretly love the attention, but don't egg it on at all, and make sure to be very professional around them.
A little harmless flirting is fine if it makes the work day easier!