Hi,
My mom and dad lived together for 42 years in a home that was in her name solely.
They never legally were married, but raised children and were together for 42 years.
My mother died and owes $120,000 for medical bills.
She was on the Oregon Health Plan and now the state says my fahter has no right to the property because there was never a legal marriage. They have filed a claim against the house through probate.
Does my dad really have to leave the house he built for my mom because it was in her name only. He is disabled so we can't get a loan to pay the medical; bills.

Not knowing exactly what medical bills are involved and also knowing that laws vary by state, it is difficult to say. But since you say the state is involved, that is often Medicaid funding involvement.

But, especially with Medicaid nursing home funding, I believe that it is standard policy for them to try and recover their (Medicaid's) funds that were expended for nursing home care. The patient's home is usually the last asset they go after.

There are attorneys who specialize in elder care law and the laws are very complex. I would recommend that your father consult with an attorney.

Sometime it is better to have your name on a deed, and some times it is not.

I don't see that your dad has any claim at all to the property.

Did she leave a will? Is he in it?

Get a lawyer ASAP, who might be able to at least hold the state off for a while.
I know a woman here in CT who took care of her mother and who had a boisterous dog. The dog knocked over either the mother or the social worker, I forget, and the daughter was ordered to immediately get rid of the dog or move out with the dog, and when she couldn't (literally within days), the mother was tossed in a nursing home and the house was sold at below market a few weeks later.
Not the same, but if the state wants to move, they can move fast, and your dad is in trouble even if she left it to him in her will.

Can they do this yes.

1. they are not married, so he has no right to the home unless there is a will.
2. her children may have a claim in probate, but not the boyfriend, remember he is just a boyfriend since they never married.

The state, esp if this was though a medicaid, or medicare program go after homes all the time for unpaid bills. But what they are doing is just making a claim to the estate, at probate for the money, if there was money in the estate, it would pay and the house would go to the heirs ( still not the boyfreind) but if there is no money in the estate, proper has to be sold to pay it.