Most Helpful Girl
With him still being wet behind the ears in years here, dear, He 'Lost that spark' because he is Not old enough really to handle a Real Relationship and may have grown bored... typical teenage guy.
It may come, being you both have this history together, that he will one day be Missing the Kissing and all that you shared and realize that what he lost... was the best chemistry he had ever had and things may even Spark up again where it will be even better than it ever had been.
If not, move on. There is someone out there who is more deserving and more mature and wants what you want and will never grow tired of the nursing and the nurturing of a Real Relationship you both become fired up over.
Good luck. xx