I didn't mean to tell you all that, but I felt like I wanted to.
I wasn't planning to let you know what was really on my heart, but I just had to.
ーI didn't mean to tell you all that, but I felt like I wanted to.
「あなたにそれをいうつもりじゃなかったけど、伝えたくなった。」
I didn't mean to tell you ... で「あなたに…を伝えるつもりはなかった」
I felt like I wanted to で「したくなった」
ーI wasn't planning to let you know what was really on my heart, but I just had to.
「本当の気持ちを伝えるつもりはなかったけど、言わずにはいられなかった。」
what was really on my heart で「本当の気持ち」
I just had to で「〜せずにはいられなかった」
ご参考まで！
カナダ 
