Background info: SO and I have a 6 month old son. SO has a 5 year old son from a previous marriage. He has had extreme issues with his ex since they split up. She constantly harrasses him and shows up late when she meets to drop off his son. The past few weekends he was supposed to stay here, there was some excuse as to why he couldn't come. Also, I do not have the greatest relationship with his son, we clash a lot (yes, even though he's 5). He has a huge behavior problem and I always end up getting stuck with the discipline when he's here which makes him look at me as the bad guy and he acts up more.
This Saturday was apparently the last straw for SO, and now he wants to fight for full custody of his son. I'm freaking out in my head, even though part of me feels like he doesn't really have a case against his ex. BUT, if he were to get full custody, I would not be able to live with him any longer. I know that I would be responsible for his other son the majority of the time since SO is always working. I wasn't ready to be a mother to our own son, let alone take on a 5 year old coming out of a broken home. I'm getting way ahead of myself, because SO hasn't even talked to a lawyer. But I'm still having a ton of anxiety over the matter. I love him and don't want to split our family up, but if this happens, I feel it is my only option. I CANNOT make it through a weekend every 2 weeks with his son let alone deal with him living with us 24/7. I don't know what to do, I want to talk to SO about it, but I don't want to come across as insensitive or selfish, I just want to tell him my feelings on the matter.