My girlfriend of 8 months has been taking day trips with a male coworker friend on the back of his motorcycle. They go to wineries, bars, sometimes dinner or a movie.
She has dated coworkers (before us) in the past, and she insists nothing is going on with him. She gets upset when I tell her these trips upset me or when I say there's a meaning or implication to her spending this much quality time with another guy - especially on the back of his bike.
I posted a much longer version of this in the girl's forum...