Showing love and affection to someone is one thing. Doing the laundry for them, serving them breakfast in bed, giving them hugs and kisses when you see them, etc. These are examples of showing love and affection. They're physical actions, so they're easy to fake if there're not genuine feelings behind them.

If you're in love with a person, however, that's not so easy to fake. You are emotionally connected to the other person, you cry or feel terrible when they express their hurt to you, you honestly miss being around them when you're not, and you make great sacrifices for them for their better interest, such as sincerely trying to give up bad habits or addictions. Sometimes these things are not so easy to detect as showing love and affection, but they can be realized through intuition and one's own feelings.

I hope that clears it up.