AITA for refusing to buy school supplies for my ex’s other kids after she neglected our son?

My ex cheated while pregnant, our son required a DNA test, I later won primary custody after documenting neglect, and now she wants me to buy school supplies for the children she had with the other man — I refused. Was I wrong?

I (30M) was married to Marin (30F) and we share an 8-year-old son. While Marin was pregnant she cheated with a man named James (33M), and when our son was born Marin insisted he was James’s child — we needed a DNA test. Because we were married I was the legal father; the test showed the baby was mine. Things got ugly: Marin involved James in appointments and the birth without telling me, and I only learned about the baby’s arrival from her parents so I could file for DNA testing, custody, and divorce.

I’m a 30-year-old dad who won primary custody after documenting Marin’s neglect and financial manipulation — she’s since had multiple children with the other man, and now expects me to buy school supplies for them; I said no and she calls me an asshole.

When my son was born I had to push for DNA testing because Marin insisted the baby belonged to James. After the test confirmed I was the father, Marin continued a chaotic pattern: James appeared at appointments and the birth, and her parents eventually informed me so I could take legal steps. Over time she and James had multiple children together — four more between them plus his older daughter — and my son was supposed to share time between households.

"When my son was born we needed a DNA test because Marin insisted the baby was James’s."

Around age 4–5, my son experienced clear neglect: he was frequently sent to me in dirty clothes, not given enough to eat, and Marin and James started pressuring me financially. I documented everything, involved the courts, and I ultimately won primary custody. My son now lives with me full-time, sees his mom every other weekend, and is in therapy because of all the instability he experienced.

"I won primary custody after documenting neglect — my son lives with me full-time."

For the past two years Marin has repeatedly asked me to buy extra school supplies to 'share' with her other kids. I have consistently refused: I supply my son with what he needs, donate to his class, and believe I am not financially responsible for children she chose to have with another man. Two weeks ago, after my son’s minor surgery, Marin confronted me again and followed me from table to table asking me to buy supplies for 'her girls' because they 'can’t afford it.' I told her: “Your other kids are not my responsibility. You already neglected our son once trying to squeeze money out of me. My priority is my child, not the additional children you and James decided to have.” Since then she’s been flooding the court app calling me an asshole and a bad father; my lawyer advised me to ignore it, so I am.

🏠 The Aftermath

After the court process I have full-time custody and provide for my son’s needs. Marin’s requests for supplies for her other children continued despite her inconsistent financial contribution and the documented neglect that led to my custody win.

My refusal has increased conflict: Marin has been angrily contacting me through the co-parenting app and publicly accusing me of being a bad father. Legally and practically, I remain focused on my son’s wellbeing — he’s in therapy and stable in my care — while Marin’s demands persist.

Concrete consequences include ongoing tension in communications, Marin’s accusations on the court app, and my decision to prioritize my son’s needs and ignore requests that fall outside my legal and moral responsibility to his half-siblings and stepchildren.

"Your other kids are not my responsibility... My priority is my child, not the additional children you and James decided to have."

I provide what my son needs and don’t press Marin about unpaid child support — I chose not to take a punitive route financially because stability for my son matters more than forcing payments. The dispute now centers on what is reasonable for me to fund beyond my legal obligations.

💭 Emotional Reflection

This is a painful situation layered with betrayal, legal fought-for custody, and the long tail of neglect. My refusal stems from a boundary informed by past behavior: Marin neglected our son when he was young and attempted to extract money from me. That history influences what I consider reasonable now.

There’s also a moral question: helping children in need is admirable, but I believe financial responsibility primarily lies with the parents of those children. I’ve chosen to focus my resources on the son I’m legally and morally accountable for, while keeping other forms of help to community or school donations rather than direct funding for kids I didn’t father and who experienced neglect from their mother.

Reasonable people can disagree: some will say compassion should extend to all kids, regardless of circumstances; others will argue that repeated neglect and attempts to manipulate finances justify the boundary I set. For me, the priority is my son’s stability and not being a fallback wallet for choices Marin and James made.

Here’s how the community might see it:

“You won custody for a reason — protecting your child’s stability and setting boundaries after documented neglect is reasonable.”

“Helping others is kind, but you’re not obliged to financially support kids you didn’t father, especially after she neglected your son.”

“If you can, offer non-financial support (school donations, supplies to class) but don’t let guilt or her manipulation override your son’s needs.”

Reactions are likely to split between empathy for all children and support for the OP’s boundary after documented neglect; many will recommend practical, targeted ways to help that don’t place financial responsibility on the non-parent.

🌱 Final Thoughts

You set a boundary based on real history: documented neglect and attempts to extract money. Prioritizing your son’s wellbeing and financial stability after winning primary custody is a defensible position.

If you want to show compassion without compromising your boundary, consider donating to your son’s school or class supplies anonymously or through school channels. That way you help children without directly underwriting choices Marin made or enabling further manipulation.

What do you think?
Would you keep this firm boundary after neglect and legal custody, or would you take on extra support for your ex’s other children? Share your view below 👇