The truth of the matter is that Hiccup has never been interested in Heather and nor has she been into him. She just took advantage of him being a nice person and manipulated the situation in her favour. What's more is that Heather ends up becoming the closest thing Hiccup has to a sister and this is acknowledged by the Race to the Edge writers. Canon-timeline.

There is a reason why Heather chooses to wear long-sleeves, why she covers herself up so much. She tries hiding it from her peers, but soon discovers everyone has problems of their own. ONESHOT, K.