2 Samuel 13:1, 15 (LXX) and the Use of ἠγάπησεν

2 Samuel 13:1 (LXX): καὶ ἐγενήθη μετὰ ταῦτα καὶ τῷ Αβεσσαλωμ υἱῷ Δαυιδ ἀδελφὴ καλὴ τῷ εἴδει σφόδρα καὶ ὄνομα αὐτῇ Θημαρ καὶ ἠγάπησεν ^G25 αὐτὴν Αμνων υἱὸς Δαυιδ

2 Samuel 13:15 (LXX): καὶ ἐμίσησεν αὐτὴν Αμνων μῗσος μέγα σφόδρα ὅτι μέγα τὸ μῗσος ὃ ἐμίσησεν αὐτήν ὑπὲρ τὴν ἀγάπην ἣν ἠγάπησεν ^G25 αὐτήν καὶ εἶπεν αὐτῇ Αμνων ἀνάστηθι καὶ πορεύου

Compare Genesis 29:20; 24:67; Hosea 9:1; 12:7; Ezekiel 16:37; John 3:16; 2 Timothy 4:10.

It's long fascinated me how 2 Samuel uses a verbal form of agape instead of using eros to describe the way that Amnon felt toward Tamar. Why employ ἠγάπησεν?

I don't think LSJ fully touches on this question, but after discussing LXX occurrences of ἀγαπάω, the lexicon states the following:

:—seldom of sexual love, for ἐράω, Arist.Fr.76, Luc.JTr.2; ἀγαπάω ἑταίραν Anaxil.22.1 (but ἀγαπάω ἑταίρας = to be fond of hetairai, X.Mem.1.5.4; ἐρωτικὴν μέμψιν ἡ ἀγαπωμένη λύει dub. in Democr.271):—of brotherly love, Ev.Matt.5.43, al.

See https://foundinantiquity.com/2013/08/17/greek-words-for-love-in-context/comment-page-1/

https://jamesbradfordpate.wordpress.com/2012/02/02/carson-on-agape-and-some-word-fallacies/

From the Greek-English Lexicon of the Septuagint by T. Muraoka, page 3 (Entry for ἀγαπάω):