Of course, love is very popular for teenagers. But love also makes them unhappy or sad from a broken heart. So my advice is, first, they both must understand each other and believe or trust. And, secondly, they must ask the reasons why.
Please do not be shy. If they do not talk with each other, their love will break down because of wrong ideas: does she/he love him/her? Does she/he hate me? Or if she/he does not talk to me, I won't talk to him/her either. These are the popular problems. Please believe me.