People lose their passion for another person for a variety of reasons. They can meet someone else, they might fear intimacy, or they might lose attraction. If I were you, I would let him go. Even if you persuaded him to come back, the relationship would likely be too one-sided to be fulfilling. Do you want to live in fear of his leaving again? Do you want to be with someone who is fickle and unsure about wanting a relationship with you?
Although six months may seem like a long time, it often takes a year or more beyond the initial honeymoon stage after falling in love, to get to know a person well enough to be able to judge whether the relationship might work for the long term. The fact that he left after six months indicates that the relationship is not right for him. So even if he does come back, the relationship is not likely to be a mutual one. Good relationships are mutual.
So instead of waiting, yearning, and hoping, find other interests, people, and activities that will interest you and make you more interesting as well. Maybe he or somebody else will take notice. At least you will be living your life instead of passing time in limbo.
by Alison Poulsen, PhD