Become a little withdrawn at the thought that if someone is flirting with you like this, then it probably happens to your partner a lot too.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