This is probably going to be long and confusing...

For the past 3 years my step dad has been cheating on my mom. Last summer, she found out about it, and they split up for a few days, and he promised it was over, and wanted to come back. I was pretty pissed off about it, but i got over it. This summer, he again, got caught cheating with the same girl. Again the same thing happened, he left for a few days, then came back. I didn't know why she let him come back. Then i went onto his facebook, and found some pretty bad messages between him and another girl. So i told my mom. this time he never left.

I have a younger sister, a 3y/o nephew (who is basically my brother since my oldest sister doesnt take care of him) and an older brother living in my house, along with my 2 parents.
My step dad has been acting like my sister's and nephew's best friend for the past few weeks. Telling my sister she doesnt have to to her homework, letting her stay up late, little things. And buying my nephew alot of new toys and Candy. He's also been ALOT nicer to my brother, and he normally treats him like shit. He's been avoiding me, because, i think, he knows he cant bribe me with anything. My mom also told me, because of some stupid laws, she can't make him leave. And she think's he's trying to get my brother, sister and nephew to like him better, so they can get joint custody, so he doesn't have to pay child support. Which would force my mom to sell our house, and she would lose alot of money.
She also told me that he has been calling her a bad mother, and putting her down alot, so she'll leave, and give him "the kids" and the house.
I hate this man.
It's getting to a point where my mom is so stressed, her blood pressure is extremely high, and she is at a serious risk for a stroke.
I feel like i need to do more to help...anyone have any suggestions or comments.
I think i covered almost everything...

Um...tell her to get the guts to tell him to get the fuck out.

That is the only thing she can do. She needs to stick up for herself and say this is my house and these are my kids, you treat me like shit so you are not welcome here.

Just help her build up the courage.

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God closed his eyes and turned his back.
If he doesn't see, then he doesn't act.

she did kick him out.
But since he owns the house too, she can't legally kick him out, and he knows this and is using it against her.
I let him know he isn't welcomed

Could she afford to get a new place?

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No.
If he doesn't pay child support, we'd probably have to move into a smaller house or apartment, which is why she doesn't want joint custody.

Have you explain the circumstances to the other kids, at least the ones that are old enough to understand? And I don't get this law....if they're married, and he's committed adultery, then that's cause for divorce. And unless they signed something in a prenuptial, then she's entitled to half of everything that's his. (Or basically enough to live an "unchanged" standard of living")

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I really don't want to stress them out with this, they probably wont have to deal with it for a few more months. And i think if anyone should tell them, it should be my mom or their dad.

I don't completely understand the law either, but basically she can't kick him out of the house, since it's half his. And they can't divorce unless both agree, and he wont until he get's joint custody, so he doesn't have to pay child support, or if my mom decides to leave.

Hmm....she should talk to a lawyer if she hasn't already.

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She told me her lawyer sent him a letter, but he says he never got it...
Eventually the situation will work it self out...but right now i need a temporary solution for stress. Ive been getting killer migraines, im normally insomniac too, but it's been extremely bad latley...and my mom is up most of the night, getting sick from high bloodpressure..

Can they maybe get a legal separation until it sorts itself out?

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