I think you don't and you cannot and you shouldn't ....reason is everything happens at a time just as you cannot solve calculus in 6th standard or become parent at age of 10, or become old at 20...similarly teenage is similar age when you are experiencing the change ...when you are not at all responsible apart from your studies... You see couples having fun and you totally prompt and try to direct you life towards love....no matter how many example you set in front of them about breaking relationship or either gender leaving better half or cheating upon, the student will not consider and just try to make a love story which is very different from others and make it successful and set a benchmark against all the odds.I think that is hell lot of positivity one can see in students...until surroundings mess them up -_- so if they understand that they are in love and understand it as a responsibility...u shouldn't make them understand too ;-)just support them and guide them right path..you stop when their motive behind love is wrong..there is enough of hatred in this world :@ -_-If they succeed in love then they can conquer much more things in life :)