Why would he choose to hurt me rather than tell me he truth?

Boyfriend did 10 years in prison. Age 16–26 for armed robbery. I was with him for his last 2 years of his sentence. I was introduced to the family, marriage was in the works and then we got into a verbal altercation at the movies where he said I embarrassed him and things were never the same. He had only been home for a month at this time, he got verbally and emotionally abusive to the point that it seemed like everything I did irritated him and disgusted him. I spent the remainder or the failing relationship trying to make up for the so called embarrassment I caused him. He made me feel so guilty about the incident at the movie, and even admitted to the fact that he knew I was hurting over the situation and said to himself ” yes, im hurting her”. The more I tried to fix things, the more he pulled away. He did a complete 180 in regards to his persona, I no longer knew who he was.To make a long story short, he turned on me and turned everyone (his family, friends) against me by making me appear crazy and clingy, all the way up to the bitter end. I asked him if there was someone else and he promised that there wasn’t. He said he wanted to just be friends until he got himself together. Then he walked away and I never heard from him again, no calls, texts, nothing. A year later he makes an announcement of his new born son. When doing the calculations of the pregnancy, it was revealed that he got this woman pregnant not even a month after he broke up with me. I was devastated and confused. There was no mention thoughout the year of him even expecting a child and the status on fb about him being single and looking for the “right woman” didn’t suggest he was in a relationship, let alone expecting a child. It just hurts because I found out that he was acting like that because he wanted out of the relationship but didn’t know how to tell me. How can one choose to put someone through all of that instead of just telling them the truth?