〜てからというもの
 

Suffering from using an all-Japanese grammar book.

This phrase is explained as: 〜てからずっと

Could someone please help me understand how this translates into English?

Suffer now. Smile later. That's the ONLY way to really study Japanese grammar. I never learned English well when I was studying it using books written in Japanese. When I switched to all-English books, I suffered greatly but after several months to a year of perseverance, my English was considerably better than my frineds' who just kept studying bilingually.

〜てからというもの is usually interchangeable with 〜てからずっと.

XXXXXXXXX ever since YYYYYYYYYY.　　〜てからというもの = YYYYYYYY

ＰＳ3を買ってからというもの、田中君はそればかりや� �ている。
Ever since he bought his PS3, that is all he's been playing.

アキコさんに出会ってからというもの、私は毎日彼女の 事を想っている。
Ever since I met Akiko, I've been thinking of her everyday.

どうもありがとう！！！