When Should You Say 'I Love You'?

In the past, I have been guilty of carelessly throwing around such a weighted word to almost every guy I had "strong" feelings for.

One of my relationships, I let the whirlwind feeling take me away and it took all but three months before I couldn't contain my feelings anymore and I blurted out to him that I loved him. And he said it back.
There are two types of 'love' in a relationship.
There's the 'Everything is Going So Well Because We're Still In The Honeymoon Phase and