My husband had an affair with my best friend, and I found out later.

We divorced, and he left with nothing...
Five months after the divorce, my best friend's period still hadn’t come. She went to the hospital for a check-up and found out she was pregnant. When I heard this news, for a moment I wanted to fall apart.
I don’t know how to face all of this. Getting divorced was already very painful, but now my best friend is actually pregnant with my ex-husband’s child, which makes me feel even more suffocated.
I don’t understand why she would do this. Doesn’t she know it would hurt me? In my painful struggle, I decided to completely cut off all contact with my best friend.
When I made my feelings clear to her, she cried with tears streaming down her face, pleading and begging me for forgiveness, but I was already heartbroken and didn’t want to have anything to do with her anymore.
And when my ex-husband found out that my best friend was pregnant
he came back again, hoping to get back together with me and face this situation together.
What should I do?