She faked the pregnancy to trap him

AITA for going through my fiance phone and finding out the baby we are expecting might not be mine. Let me explain everything from the beginning. My name is Megan and I am twenty eight years old. I have been with my fiance Daniel for three years. Six months ago we found out I was pregnant. We were thrilled. We planned the nursery. We picked out names. We told our families. Everything felt perfect. Last week Daniel left his phone on the kitchen counter while he took a shower. It buzzed over and over. I am not usually the type to snoop but something told me to look. I saw a string of messages from a woman named Priya. The messages went back almost a year. They were not just friendly. They were intimate. They talked about meeting at a hotel near his office. They talked about missing each other. My stomach dropped to the floor. I kept scrolling with shaking hands. Then I found a message from three months ago that nearly made me drop the phone. Priya had written that she was pregnant too and that the timing lined up with their last meeting. Daniel had replied asking her not to tell anyone yet because he needed time to figure things out. Figure out what exactly. I sat on our bed holding his phone feeling like my entire world had cracked open. When he came out of the shower I held up the phone and asked him to explain. His face went white. He tried to grab the phone from me but I pulled back. He started talking fast, saying it was a mistake, saying it meant nothing, saying he was going to end it. I asked him the only question that mattered. Is there a chance that baby is yours. He went quiet for a long time. Too long. Then he admitted it was possible. I felt like someone had punched me in the chest while I was already pregnant with his child. I packed a bag that night and went to stay with my sister. I could not even look at him. The next morning Daniel showed up at my sister door begging me to listen. He said Priya was someone from his gym and it started after a bad fight we had about wedding planning last year. He said he never meant for it to become anything serious. He said he tried to end it twice but she kept pulling him back in. He said when she told him she was pregnant he panicked because he did not want to lose me or our baby. I asked him why he never told me any of this before I found the messages myself. He said he was a coward and he was scared of losing everything. Here is the twist that changed everything though. Two days later Priya herself showed up at my sister house. I was shocked. She said she needed to tell me something face to face. She told me the pregnancy was fake. She had lied to Daniel to trap him into leaving me. She showed me her phone, no baby bump, no doctor appointments, nothing. She admitted she panicked when he tried to break things off for good and made up the pregnancy out of desperation. She said she felt sick about it and could not keep lying anymore. I did not know whether to feel relieved or even more furious. Daniel had still cheated for almost a year. He had still kept secrets from me while I carried our actual child. The fake pregnancy did not erase the real betrayal behind it. Now Daniel is begging for another chance. He says he ended things completely with Priya and blocked her everywhere. My sister thinks I should leave him immediately and never look back. My mother, surprisingly, thinks people deserve one chance to fix their mistakes especially with a baby coming. I am due in three months and I still have not given Daniel an answer. Some days I think about raising this baby on my own and starting fresh. Other days I remember the man who held my hand through every doctor appointment and picked out onesies with me at midnight. I genuinely do not know if forgiveness is possible after something like this or if I am just scared of starting over alone with a newborn. So tell me honestly, would you ever take someone back after a year long affair even if the pregnancy turned out to be fake, or does the lie itself make forgiveness impossible no matter what the truth ends up being.