Whether it's on social media or on stage at the reunion, one conflict is not going away.

Amber Portwood despises Kristina Shirley and blames her for, well, just about everything.

This explosive, very one-sided conflict has been playing out on screen and off of it.

Why exactly does Amber hate Gary's wife so much?

Let's start at the beginning ... well, no. Let's start several weeks ago.

On the Tuesday, March 30 episode, Gary and Kristina were helping Leah plan her birthday party.

Specifically, they needed to hammer out plans with friends and also plans for family.

Leah was relatably enjoying some string cheese when she shared her birthday aspirations.

“I want to do something with friends and go shopping and get our nails done and go to lunch,” she reealed.

Then, for the family gathering, Leah wanted to invite Gary, Kristina, little sister Emilee, and grandma Tanya.

Despite everything that she's put him through, Gary is a cooperate co-parent.

He quickly reminded Leah about Amber. Leah was ... not enthused.

"I don't want to," she protests about inviting her mother to take part in her birthday plans.

"I'd tell you it's really important that, you know, you spend time with your mom," Gary suggested.

Leah was not feeling the same vibe.

She gracefully replied: “We don’t really have a bond like that."

"Twelve years and she hasn’t really done anything," Leah pointed out.

When it comes to actual maternal figures, there was someone doing those things for her.

Or, as Leah phrased it at the time: "That’s kind of been like Kristina’s spot.”

Amber's absence wasn't just disinterest ... but that's not really a defense of her.

Amber has a whole criminal history. She served 17 months behind bars from 2012-2013.

Even now, Amber is currently on probation for her latest attack on a baby daddy -- Andrew Glennon.

Kristina was quick to remind Leah: "I'm just the bonus mom, though."

Gary added: "I don't want you writing your mom off and saying 'I can't have a relationship with her.'"

His dream, he said, was that "at some point" Leah would be on good terms with her mother.

Leah had a scathing but not unfair view of Amber's role in her life.

“All she did was just give birth to me and then just kind of left," she characterized.

Gary disagreed: "She might not have always been there, but she was there."

Gary vocally feared that Leah might end up "missing out" on a bonding activity with Amber.

He suggested her birthday party as an opportunity to make up for lost time.

Gary reasoned that his daughter "won't have what [she] missed" unless she gives Amber a chance.

Leah, being a bright and reasonable young woman, relented.

"I guess that maybe she can come to the family party," she announced.

Gary immediately texted Amber to invite her to attend.

Of course, it was all for nothing -- thanks to Amber.

She elected to not go, wanting to spend one-on-one time with Leah instead.

But she saw Leah's reluctant moment on screen ... and flipped the eff out.

"When you’re a whore, you’re a whore!" Amber declared on Instagram Live.

Fortunately, she was not talking about Leah. Unfortunately, she was talking about Kristina.

"When you’re a homewrecker, you’re a homewrecker,” she spat. “When you’re a liar, you’re a liar."

“I was told that when I got out of prison, I would have my family," Amber ranted.

"All the while I was being cheated on,” she accused, though it's unclear how Kristina could be at fault for that.

“I’m not jealous of Kristina, there is nothing about Kristina that even makes me jealous in any sense," she claimed.

“I try to invest time with Leah all the time, all the time. It’s all I ever do," Amber insisted.

“[Kristina] doesn’t take care of my daughter," she claimed, seemingly referring to finances.

"No, Gary does not clothe her, feed her," Amber declared. "Gary wouldn’t have a job if it wasn’t for me in the very beginning.”

Now, Amber did seem to cool down enough to leave a touching message for Leah in a public Instagram post.

“I know you are going through a lot and there are many things I need to do to make things right,” she expressed.

Amber then wrote: “However, I will always love you, my beautiful daughter.”

Of course, Amber also went on a rant about how one never sees Kristina's daughter on Kristina's Instagram.

Kristina's daughter is a minor and not a public figure, something that Amber ensured Leah would be.

It is not unwise for Kristina to keep her daughter's face off of Instagram, but Amber saw it as some sort of failing.

At the reunion, Amber praised Gary: “You’ve always been there for me when I’ve asked you to be there for me."

"You said I could trust you and I did trust you," she noted.

"But I can’t trust your wife," Amber spat, "and she has sat there and got in the way of me and my daughter [over and over]."

“That was amazing to actually hear you sticking up for me, but your wife is absolutely horrible at it,” Amber insisted.

“I really hope in the future we can have a good relationship," she claimed.

Amber then expressed: "But me and Kristina … it’s not going to be like that.”