Your story is like mine and like so many others. Minor details are different, but the manipulative tactics are the same. Read past posts, then read more. Every day, every week, there is another similar one. Sometimes, even when advised not to, we have to make our own mistakes. This is one time you don't want to. All that lies ahead is more pain. Your trust is broken. You have doubts and suspicions. These will haunt you.
You sound like you are a strong woman. Gather up your self-respect, hold your head high, admit you made a mistake, take time to heal and continue raising your son. He is the one that needs you, not this grown man that lies and cheats.
I, like all here, understand the hurt, sadness and overall injustice. It's not fair that we give our trust and take risks to love only to have it squashed by the one person we held so close to our heart.
I just wasted a whole year trying to hang on to a relationship that was sour from the start. I wanted to have faith in our "love" that was so "special". But when one scrapes away all the sugar coating, it's the facts that are left--plain, simple and basic.
You will find a lot of support here, whenever you are in need. Always look for the positive, no matter how small it may seem. Take care.