Cheated

What do I do? My fiancee recently told me that when we first started dating, we were long distance, he cheated on me. I'm relieved that he told me instead of me finding out on my own. But I'm having a really hard time trusting him, as to be expected. We are currently planning on getting married in August. Do I continue wedding planning if I'm struggling with something this big? He is a very kind and generous man, and he told me so that there would be no secrets, but my trust is broken. His inability to say no is so innately who he is that I'm worried that 5-10years down the road he will end up in the same type of situation.