Relationships with coworkers. Your stance?

Here's the deal. My trainer is FINE. F. I. N. E. Fine. Yesterday I started my "hands-on" training and we were working together all day. Got to know each other a bit, and it was clear we both had a flirtatious attitude towards each other. Knowing she'd be training me all day again today, she comes to work with this low cut top. I was...distracted. I still learned a lot, but we definitely could have been more productive. I've looked at her left hand for two days now to be doubly sure I'm not trying to taste a forbidden fruit, no ring. There's also been nothing in any of the training I've received in my first two weeks saying co-workers can't have relationships outside of the office, but I was wondering if there were any of you that have had experiences with co-workers in the past. Would it ultimately cause more harm? I'm looking to move up within this company and I want to keep that obtainable. Anyway, I've already rambled more than I wanted to. What are your opinions? Would this be a no-no?