...And He Walked Away...

Me and my girlfriend have been together for five years. We're happy overall, but one night when we were apart, a colleague from work came over unannounced. We ended up hooking up really quickly, without thinking too much about it at the time. It was just this instant chemistry that felt like nothing I ever had with anyone else before... even her. But he left soon after and I haven't seen him since then. Part of me is still buzzing from how amazing it felt, but mostly? I feel really guilty knowing how badly I screwed up.