I’m sinking in unrequited love.
I'm super sad because I made a dent on my new car already.
This word consists of kanji with hiragana attached. Because the hiragana ends with an う sound, you know this word is a verb. The kanji itself means hollow, so the verb version is to become hollow and to sink
Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You didn't learn that reading with this kanji, so here's a mnemonic to help you:
You feel like you've started to become hollow when you have a head cold (へこ). You may be all stuffed up, but it's making you so sad that you feel hollow somehow.