Each bird in the nest loves the guy with the moustache from the bottom of its heart. (he feeds them worms, and if that isn't what love is all about, I'll eat my hat)
love or relationships in general - that is to say, if there's an ad for fortune-telling that says, "Test your luck in money! Love! and health!" it'll be using 恋愛. If there's an article in a womens' magazine, "How to get love in 10 steps!" it'll be using 恋愛. But you wouldn't tell a hot guy " I 恋愛 you very much!" See?