How can I tell if he's fallen out of love?

I've been in a relationship with a guy for about a year and a half now and he just deosn't seem to be that into me anymore. He used to be so loving and always hugging and kissing me but now it's just kind of as if I'm not that important to him anymore.
I know people will say it's because the 'honeymoon period' has worn off but I don't think it's that.
I'm thinking of asking him if he doesn't love me anymore and whether we should stay together but I have a feeling he will just shrug it off and tell me I'm being daft. Then I'll be back at square 1.
I don't want to be in a relationship with someone who is just going through the motions.
What can I do to find out how he really feels?
What can I sayto start the conversation off without sounding immature? That's if I decide I want to have the conversatio because heis no good at talking about his feelings.

Sometimes guys, do not per say fall out of love, but maybe just the honeymoon part of it is over in his mind. I know when I am in relationships, it comes and goes. Usually monthly, one month I may seem a little distant, the next I am lovey dovey. Nothing personal, but I would say it happens in most relationships, and happens to both guys and girls.

People tend to get complacent when they're in relationships for a while. It becomes habit. Is your relationship dull and boring?