If you've been ever sexually/romantically intimate with him, even once, only verbally or drunkenly, that counts.
He likely has 'Your Relationship' Filed away as being:
'Intimate Partner; Past, Present (on Hiatus), Future'.
Going from 'Female I Know' to 'Female I Like' to 'Female Friend' to ' Female Best Friend' is good desireable upwards progress for a Guy.
Going from 'Female Intimate Partner' (of any duration) "downward" to any of those, is a Death Sentence. There are too many fantasies and what-ifs built around you.
IF he were actually Mature, he could likely accept the Grand Title of 'Guy BFF'. He's obviously too horny / immature to tone down his dreams and Happily Accept the role. Being a Buddy, Protector, Wingman, Confidante, Advisor, Crying Shoulder, Bug Killer, Barf Time Hair Holder, Phone a Friend @3am, etc.
And since HE broke it off, it's probable that he had "cold feet" issues with getting too closely involved, the was another Intimate possibility and he still wanted to "Play"
TLDR ANSWER: Cannot be Platonic because the Fantasy of Physical Intimacy is still strong.