No, I do not think that Jay Gatsby is in love with Daisy. I think he may have been in love back when he met her as an army officer before the war. But I'm still not 100% sure if he truly loved her then or loved the idea of her and her grace, charm, and wealth. But based on his initial experiences with Daisy, yes I do think that Gatsby does know what love is. I just don't think that he still truly loves her. . . just the idea of her.
After the war, Gatsby attended Oxford in order to gain an education. Daisy ended up marrying Tom, and from that moment forward Gatsby's single-minded goal was to become wealthy enough to win her back . . . by any means possible. Bootlegging built his fortune, so his money isn't exactly clean, legal money. He bought a ridiculous mansion on West Egg to be closer to her. He throws these huge, lavish parties for rich people just so that she would attend. He uses Nick to help him set up the perfect meeting with Daisy (who is Nick's Cousin). He takes the fall for the car crash. I suppose that you could say that Gatsby does all of this out love, but I don't agree. Gatsby treats her more like a prize to be won, or a conquest to be victorious over. It's obsession or infatuation or something similar. It's not love.