I find Google Translate as a really good French-English translator, but I agree with your doubts, online translators are only machines. Context is always very important, so if you put only a single phrase, it's somewhat difficult to translate it exactly as you want it to be translated into French. It can even lead to some misunderstandings, but your phrase can be translated into something like:
"Le bel amour de ma vie", but it doesn't sound good;
"Le grand amour de ma vie", or just
"L'amour de ma vie"
However, I think that a native French speaker could clear all things up and provide a perfect translation
