Some RL drama for you

There are 4 kids
Jane- the culprit
Mary- the crazed chick in love
Donna- the innocent bystander
John- the heartbreaker

Mary has been in deep like with John for many years now, and John sporadically returned those feelings, but in short spurts. Jane, Mary, and Donna are best friends, and have been longer than Mary and John have been, you know, Mary and John.

So it was John's birthday, and Donna invites John, Mary, and Jane over for a party. Mary arrives first, and she and Donna begin to prep a birthday cake for John. John arrives second, and hangs out with the two girls until Jane arrives fashionably late.

Jane and John have known each other longest and were never incredibly close, but had recently blossomed a close and innocent (enough) friendship. They hung out for most of the party, but would occasionally look up from the episodes of Smosh they were watching on John's ipod to notice that Mary and Donna were gone. They had figured they were going to check on the cake.

This happened maybe 3 times throughout the "party" and for durations of over 15 minutes at a time, and every time Mary would come back downstairs, Jane and John noticed her getting angrier and angrier. The last time Mary came downstairs. She noticed Jane and John... closer... than usual, which began to fill her with rage.

When Donna announced the cake was ready, everyone piled upstairs to eat it. This was the time that Jane and John were discussing what he wanted for his birthday (this was only a small party, a larger party was to be held later in the week). This caused Mary to explode emotions.

As John stormed out with rage, Mary began accusing Jane of "liking John" and "ruining her chances". That Jane was "Flirting" and "It needed to stop". If it weren't for Donna's athletic practice, Jane and Mary probably would've killed each other.

My only question is, whose fault is it?
Jane and her flirtatious tendancies but innocent intentions?
Mary and her confused teenage girl crush?
Donna and her bystanding attempts to calm the two?
or
John and his unknown desires?

Tell me below o_O