My husband cheats me with my best friend

Hello,
My heart is broken and I miss words. I am a woman wounded and betrayed by two beings I loved. It’s been five years since I was married to Thierry and we have a child together. And, I thought everything was going well in my relationship. It is true that for some time, because of our respective jobs, we had little time to devote ourselves. You know with the vagaries of life, children, we spent less time together. I met Thierry at the university. He was tall, intelligent, handsome and he made me laugh a lot. We dated for two years. Then one day he started and asked me to marry him. Without hesitation, I said “yes”, I thought at that time that our life was going to be magic, knowing that everything is never rosy in a couple.
How could I have imagined 30 seconds that my husband would deceive me with my best friend? I feel like a fool of service. How come I did not see anything? I continually ruminate this story in my head. I try to understand how, why did they do that to me?
My best friend is called Judith, we’ve known each other for 15 years. She is or was like a sister to me. With her, I share all my secrets, all my sorrows, all my joys. I can not imagine that after these years of friendships, she did not hesitate to sleep with my husband. She did not hesitate to maintain a relationship with him for more than a year. But, why, dear ones are so cruel sometimes? I had noticed that my husband had changed. He kept saying that the work had exhausted him and he wanted to rest. He came home later and later did not really care about me. And when he was at home, his phone kept ringing. And when I asked him for an explanation. He told me it was his mother, his sister, or the job! Like an idiot, I swallowed everything he said. For me, the basis of a couple is trust. So why worry?
Then, one day, my husband forgets his phone at home. The phone starts ringing. I hesitate to answer. And the ringing stops. The person sends him several messages. Curious, in doubt, I decide to look at his sms. And there, the shock, I discover sms of love between my best friend and my husband.
” I love you my baby. “
” I miss you. “
” I want you so much. “
I an deceived. He laughs at me or what. I just want to chop that bitch and burst her head. But, it is not worth it. I prefer to zap it definitively of my life. I am waiting for my husband to come home and I ask him for an explanation. He does not deny anything and confirms being in relation with my best friend. I am disgusted. I scream, I scream, I’m completely distraught. I want to break everything. He apologizes, tries to calm me down and tells me he’s going to end his relationship with her. He explained that he felt lonely and that is why he went to console himself in his arms. But, frankly, he laughs at who? I’m always there for him. Sure, I work, but I take the time to take care of my man and my children. It is he, who is always tired and who does not want to do anything. That’s right, we did a lot less in pairs. Well, that does not warrant anything.
What’s wrong with me? Why did they do this to me? I feel so guilty. Does having a job make me less attentive to my husband.

In your opinion, what should I do? Should I forgive him? I am seriously thinking about divorce, but how am I going to do without him? I still love him and I wanted to grow old with him. How can we explain to our child that Dad and Mom will part?
If you have any advice, do not hesitate, I really need it.
Thank you in advance for your answers.