godan verb (-mu)
drown; get addicted; become infatuated
Literally 'to drown into', used for both literal drowning and figurative absorption in something (addiction, infatuation). Often followed by ～に.
彼は川に落ちて溺れ込んだ。
He fell into the river and drowned.
彼女はギャンブルに溺れ込んでいる
She is addicted to gambling.
彼はその女性にすっかり溺れ込んでしまった。
He has become completely infatuated with that woman.