你可以直接表白：

Will you marry me? 你愿意嫁给我吗？

Would you be my wife? 你愿意当我的妻子吗？

你也可以表达的含蓄点：

Let's tie the knot!我们结为连理枝吧！

I want to spend the rest of my life with you.我要与你共度余生。

Let's be a pair of lovebirds! 让我们做比翼鸟吧！

I think it's time we settled down... 我想是我们该稳定下来的时候了……

如果一句话表达不完，还可以用段落式：

Marry me. Make me the happiest person alive. Please, give me the honor of sharing my life with you. I love you and nothing means so much to me as being with YOU.

Marry me. I promise... I will always love you.

Will you marry me? Will you be mine for life? Will you walk with me? Will you laugh with me? Will you cry with me? Will you share with me? Will you love with me? Will you be with me? Will you marry me?

Sometimes you get lucky. Sometimes you meet someone. Sometimes they are special. Sometimes you want to be theirs. Sometimes nothing else matters. Sometimes you find... Sometimes is not enough. Sometimes you want all-times. Will you share your times with me? Will you marry me?