When we lose someone to death, it works on our subconscious minds as much as it does our conscious mind. We lose something valuable, a love we have cherished, so that is reason enough to dream about this person who has passed on. There is no time limit on these type of dreams. Perhaps something happened recently which triggered a memory of your ex. You may not even remember what it was, but you wake up several times and went right back into the same dream subject matter. So your subconscious mind is bringing him forward, for a reason, maybe his birthday, his death anniversary, or Father's day, which is tomorrow. You may never know what triggered the dream. Just accept it, as a kind of gift, as it seems it was a good dream to remember him.