What would you do if you found that your close friend's girlfriend loved you?

Absolutely nothing! Don’t make this mistake, regret is what you will get. If you like the girl, you loose a friend, if the girl moves on, you’re a single guy without friends.

Sounds though, but better be honest to your friend. Tell him if you’re sure about her advances. He won’t like to hear it, but it’s better for him. He’s better off with someone who truly loves him. And yes, you might miss out on a girl, but if she’ really crazy about you she’ll come back later in your life. It’s not worth loosing a friendship.

Back off from the girl, stay aloof, and try to avoid her with out being obvious.

Tell your friend if her behavior continues.

DON’T tell your friend. The messenger always gets his ass kicked. Stay away from her, and listen to the first part of what Jax and Amuph said.

A little more in depth on what the people above me have recommended primarily the do nothing part.

FIRST if he’s your friend you should be his friend, the girl’s not worth it!

Here’s why she’s with your friend and loves you “opportunistic”. You either want to be with someone or not. If your still with the person you want to replace then your expression of love is a lie.

What makes you think her expressions to you are not a lie or will not become one in the future.

She does not respect your friend or herself. She’s on a path of the next best thing and there will be another after you as well. If she doesn’t respect your friend how could you trust her to respect you.

If you choose someone who would switch from one friend to another then you don’t respect yourself either, or your willing to forgo a close friendship for one that is destined to be brief and thoughtless.

I’m a girl and I’m telling you to keep the friend and ditch the girl. If she’s willing to do this to your friend she’ll do it to you.