LiAngelo Ball's Baby Mama Claims He Got Another Woman Pregnant

5:24 PM PT -- LiAngelo Ball just posted a picture with Rashida Nicole ... seemingly making them Instagram official after Nikki Mudarris accused him of abandoning their family earlier in the day.

LiAngelo Ball is dealing with some baby mama drama ... the mother of his 2 children claims he is walking out on their family after getting another woman pregnant and starting a new life with her.

The "Tweaker" rapper and basketball player has two kids with Nikki Mudarris ... and the reality TV star claims LiAngelo just confessed to cheating on her.

Nikki says ... "I see everyone has been sending me @gelo cheating on me. I want to clear this up and speak my truth. I am just as surprised as you are. We spent 3 1/2 years together, and last week he decided to walk out on his kids and tell me he got someone else pregnant (allegedly) and now is creating a new life with her."

LiAngelo and Nikki just had their second child, a daughter, in December ... and they also have a 1-year-old son together.

Nikki adds ... "The ultimate betrayal is not even the word. My daughter is not even 2 months old, and dealing with this and postpartum is very hard. Please pray for me and my healing because I will get through this. I have to be strong for my kids, but I have absolutely no words."

She also takes some shots at LiAngelo ... "Karma is real and God don't like ugly. I hope it was worth losing his family." Nikki has since gone on her stories to claim he broke the news to her via text, blasting him as a "coward" and "pathetic."

LiAngelo's rap career is blowing up thanks to his "Tweaker" success ... and he's just been tapped to perform at the upcoming NBA All-Star Game.

Unclear who LiAngelo's new alleged chick is, but Nikki says the woman is older than her. Nikki also has a message for LiAngelo's new flame ... "The same way you get them is the same way you lose them, thinking you winning by getting pregnant with a man who has a newborn is crazy work."

We reached out to LiAngelo's camp ... so far no word back.