having you in my life makes it complete.

这是动名词短语 having you in my life 作主语的书面语，口语句首多用形式主语。这句话的字面意思是 “一生有你使得它完整” ，有中文表述的遗痕，应该改为 It makes my life more perfect to have you with me forever (永远与你在一起会让这一生变得更完美).