Veranadine's interpretation is certainly one way your dream could be viewed and I don't want to discount her interpretation, but I will, with all due respect, offer another:
Water is often representative of Spirit, or the Spirit World. The marina could be seen as the starting point of a spiritual journey or meeting point of the physical world and spiritual world.
The man you felt such comfort with and with whom you have history may likely by your Spirit Guide or Guardian Angel.
This is supported by the fact that you then take a boat trip with him into the spirit realm.
During this trip, you are afforded the opportunity to divest yourself of something that no longer serves you and give it to the Mother to be taken away and devoured, never to bother you again.
The fact that you asked for a Medicine Dream leads me to really feel that this man was a Spirit Ally. Like I said, either a Guide or Angel.
All in all, a very positive dream I'd say.
Keep asking for, and start learning to become lucid during your dreams. It will open a whole new realm of possibility for you.