This is a jukugo word that uses the on'yomi readings of the kanji. You learned this reading with the word 追随, but here's a mnemonic to help you just in case:

You're mourning the loss of your pet bird. You can't help but yell TWEET (つい) to the sky, hoping she'll come back to life. It doesn't work so you stay in a state of mourning for the rest of your life. She was your best bird friend, after all.