Is it fear that make man hide things or emotional attachment they can't understand and justify as friendship to cover their emotions?

My boyfriend and I were about to get engaged when something shook our world. His female coworker, whom he introduced as a good friend, initially seemed kind when we met. However, two months ago, her boyfriend approached me, suspecting an emotional affair between them.

My boyfriend is a dream partner—caring, hardworking, and always trying to make things right. However, I was shocked to learn he had been omitting details about their interactions. They had lunch together daily, sometimes in a group but three to four times alone. They shared homemade food, and he even cooked for her twice—something he does only for loved ones. They watched thriller movies during office breaks, and their regular chats after work unsettled me.

Despite this, I found nothing suspicious or flirty. He mentioned me in their chats, often expressing how much he needed a good job to marry me. She even advised him on our fights and helped him secure a permanent position. Still, past fights over his female friends made him stop sharing details. While colleagues saw them as just friends, their boss and her boyfriend found them too close. Was he just scared to tell me, or was there an emotional affair?

Updates
1 y
Well few things that made me doubt:
1. I admit my insecure controlling behaviour which made him hide things but I never saw him being so caring to any female friend other than me.
2. Even though he hide, deleted chats I found nothing suspicious when I got chats. Also he gave his 100% to convince my family.
3. He was very respective towards her relation and never did anything flirty or harmful to intentionally ruin her relations and also tried to be close to her boyfriend during their friendship.
Is it fear that make man hide things or emotional attachment they can't understand and justify as friendship to cover their emotions?
Post Opinion