All of the above are good answers; but, I have had all those said and done to me and it wasn't true love! Forgive me for being a little synical; but, I think it's got to be divine intervention and maybe a little luck. God knows who is right for you so PRAY!!!
When he tells you that he loves you, you can see it in his eyes. The caringness and sweetness in his eyes should help tell you. Also when he says it he'll probably say it with a smile and hug you and hold you and stuff like that. And if he looks straight into your eyes, that's another huge way to notice.
Sorry to break your bubbles people .. but him just saying the words, or looking deeply in to your eyes .. Is NOT an indication that he means what he is saying. Perhaps in a perfect world. In reality .. nope .. that's not even close. Anyone who can manipulate can do any of those superficial things to try to convince you the are soooo in loooove for one reason or another .. THAT is not necessarily a good indication of truth. They may feel 'something' for you, but rest assured .. it's not love.