我会珍惜我们所有的回忆，因为那些和你在一起的日子，是我一生最幸福的时光。翻译成英文

我会珍惜 我们所有的回忆
I "ll cherish all the memories about us .（all our memories ）
因为 那些 和你在一起的日子
cause the days with you
是我一生最幸福的时光
is the happinest time in my life.
或者后两句翻得生动一些还可以译成：The hours I spent with you were happiest of my life.(用hour显得再一起的时间更令人珍惜)
整句话就是
I "ll cherish all our memories .Cause the hours I spent with you were happiest of my life.
希望可以帮到楼主~

I will cherish all our memories, because those with you day is the happiest time of my life

是I will cherish all our memories, because those with you day is the happiest time of my life