Hey I found this song translated online, at a really cool blog. The person there has translated other Korean songs too. They even teach some grammar after each translation. Check it out here: http://koreanthroughlyrics.wordpress.com/2009/11/02/lesson-8-stillas-ever/
Edit: Now that I look at it, the English in their translation isn't too great. :S
So, I tried translating it too... I also found different lyrics... which I think make more sense... 이제는 다 말할수 있다고 not 이제는 다만 알 수 있다고.
사랑은 하나 인가봐 - It seems there's (only) one love.
내맘은 변치 안나봐 - It seems my heart won't change.
널 향해 지켜온 사랑 이제는 다 말할수 있다고 - The love I've kept safe for you, now I can say it...
널 사랑해... - I love you...