A man in love is a doer, not a talker--whether this means pulling a bunch of wildflowers for you, making you breakfast in bed or putting up with your Aunt Sue when she comes to visit for three weeks. A man in love is not someone you need to spend a lot of time second-guessing: men aren't that complicated.
Watch his behaviour. Men in love are probably easier to read than women because they don't spend hours dissecting the relationship with their buddies. A man in love, out of force of habit, will do things to show he cares: pull wildflowers from a meadow in Yosemite, get a tattoo with your name on it, buy your favourite frozen yoghurt (extra points for bringing it to you when you didn't ask for it) and spending time with your family.
Pay attention to his body language and facial expressions. If he is scrunched over and scowling, looks bored, is constantly checking his cell phone or similarly distracted or showing annoyed mannerisms, then you know he's not in love. You don't really need someone to tell you that.
A man in love should be engaged with you, stare deeply into your eyes (unless he's shy, in which case he will look away, but still be engaged with you), touch you lightly on the arm, shoulder or hair and smile when you smile. A man in love feels your rhythm and mirrors it.
Test the waters. It's always best to let the guy tell you he loves you first, but you can gauge his level of interest with comments that question his future interest. If you can't get him to commit to a party you're having a month from now, that's a very bad sign. But if he's already asking if you like to snow ski, and you just met in the late spring, this is a keeper.
Feel his touch. A man in love will touch a woman's face, cradle her chin in his hands or brush a hair from her eye. A man just out for a romp in the sack won't indulge in tender touches such as these, especially out of the bedroom. If he has to at least hold your hand or fingertip in public, he loves you.
Listen to your heart. You'll know if he loves you. The hardest job we have in life is probably letting go of someone who does not love us. We all want to be loved so badly that we oftentimes project feelings and behaviours onto people who don't deserve our adoration. If you are suffering--calling your friends for information, running over every comment he's made or crying yourself to sleep--he does not love you.
Ask your closest friends to tell you what they honestly think of him.
Don't scare a man off by encroaching on his space. Don't confuse lust with love. If he doesn't discuss the future, he is not interested in having a future with you.