I heard about Pisces that they are faithful,if they are in love..How can I make that happen?

I met a Pisces, he reeally is into me.2 years ago, when he was 19, he proposed. Is that normal? Now we met again, and he wants to hold onto me..and if I would have a relation with him, I would want him to be faithful. I'm a Taurus btw. But i heard that they are faithful oly if they are in lve. How can I be sure, that he would love me for sure, and not only think that he is in love, (that platonic love)and then leave me?