To me, the main question is .... are you honestly willing to risk your 12 year relationship, just for the sake of a one off meeting, whether sexual or not with what is in reality a total stranger (seeing as people can lie about absolutely everything online). Perhaps you need to have a look at the TV program "Catfish". It might just give you a clearer view on some aspects of this. But again, why on earth would you deliberately hurt someone who has been your partner for the past 12 years? Put the effort in to refresh the love you two have and if you no longer have this love, then try to amicably break up with him, rather than cheat on him. It is a far more honest way to handle it.