Another angle is the way Jonadab son of Shimea King David's brother suggests the method of sin to Amnon. This is Amnon and Tamar's first cousin. The same passage points out that he is cunning, or as we might call it- sly. KJV calls him subtil. (old term we now call subtle) but in KJV English carries a negative connotation. Subtil like the Serpent in the Garden.
He is friends with Amnon. Instead of counselling Amnon to avoid his half sister, and avoid temptation he stirs the pot and gives Amnon a ready made plan. Really satanic if you look at it.
The key is the words for love which are all one word in English so it's not helpful. Greek has 8 different words to describe different types of love and Hebrew has 4.
the one used is ahab, Strongs H157
'âhab 'âhêb
aw-hab', aw-habe'
A primitive root; to have affection for (sexually or otherwise): - (be-) love (-d, -ly, -r), like, friend.
Like our word for love it can be an intense sexual feeling, or it can be an intense like for a brand of coffee. The meaning of it depends on context. The overarching meaning is that it is intense, overwhelming. I got that from several other sources when I googled the Hebrew word.
It was so overwhelming to Amnon that he was "vexed" which is the word here AND HERE'S WHERE I think the CRAZY comes in. This guy is mentally ill. He has a violent emotion that he can't control. Something is wrong.
tsârar
tsaw-rar'
A primitive root; to cramp, literally or figuratively, transitively or intransitively: - adversary, (be in) afflict (-ion), besiege, bind (up), (be in, bring) distress, enemy, narrower, oppress, pangs, shut up, be in a strait (trouble), vex.
and his friend Jonadab notices - Jonadab is described as
châkâm
khaw-kawm'
From H2449; wise, (that is, intelligent, skilful or artful): - cunning (man), subtil, ([un-]), wise ([hearted], man).
and the sentence Jonadab uses to describe Amnon is "weak, dangling" from day to day.
Since the passage explains that once Amnon raped his half sister he was overcome by an opposite feeling- hatred it confirms that the guy had a few screws loose in there.
That word for hate is Strongs H8130
śânê'
saw-nay'
A primitive root; to hate (personally): - enemy, foe, (be) hate (-ful, -r), odious, X utterly.
Taken as a whole what the Hebrew is saying- translated love means an overwhelming attraction to something or someone. It is not a word to describe love as much as it describes intensity.
So if we remove our word for it as "love" and look at the intensity, we see in context with the rest of the passage it's describing an evil madness that is overcoming Amnon, and that his friend and cousin Jonadab being "subtil" which is another interesting term. I think it's used to describe the serpent in Genesis.
Taken altogether this is not love, it's obsession, and it's egged on by Jonadab and carried out by Amnon who immediately flips to the opposite emotion of hatred.
From being overwhelmed by attraction to Tamar he is disgusted by her presence and sees her as an enemy.
Descent into madness. No love there.