Hi Kay! I will hopefully be able to help you today. First we can talk about dreams in general :)
According to Carl Jung, dreams are a way of communicating and acquainting yourself with the unconscious. Dreams are not attempts to conceal your true feelings from the waking mind, but rather they are a window to your unconscious. They serve to guide the waking self to achieve wholeness and offer a solution to a problem you are facing in your waking life.
I think that you are working through your desires in a safe manner in your dream. You pick up on your attraction to him in daily activities but you also know that there are barriers in place. He may engage in flirtatious behaviors with you, but it may be more about how you are responding to that body language, that is coming through in the dream. Maybe it is more about what you "wish" would happen, but there are boundaries in place (girlfriend, work place relationship, etc).
Im curious if you have gone through a recent breakup? Because the symbolism may suggest that you are in need of that closeness with someone. You have had several positive interactions with him, but there is still much left unknown. To dream that someone is hugging you suggests that you need to let down your guard and allow your true feelings to show, but it also means that you need to allow yourself to heal emotionally. This dream may be triggered by some major change in a recent relationship and how far you have come from those past relationships. To dream that you are kissing someone who knowingly has a partner indicates your wish to be in a relationship and to experience the energy of love. Perhaps you are somewhat jealous? You may be sexually acting out and desire to awaken your passion.
Given the circumstances of him having a relationship, I would be leery of acting on my feelings. I would allow some more time to go by before I verbalized anything just yet. Allow a natural progression of events before moving too quickly......