Warning long read!

My ss 7yo bm is a diagnosed bipolar. We are starting to see some scary issues with my ss as well. Let me give you the background details. My ss lived with his bm for about 4 years. She moved all over the USA with him. She couldn't give him a stable environment, and couldn't handle him. They way they were acting out towards each other became an awful situation for both. It got to the point where her home was not a safe place for them and she understood this and just lost it. She begged that we please take him off her hands and he moved in with us full time for the past 3 years. He finally had stability etc. ss went from seeing his mom all the time to her seeing him sometimes every weekend sometimes not (her choice) she never showed up at his extracurricular activities or anything. When he moved in with us he said he was happy and didn't miss his mom at all when we said we know this is a big change and must be hard for you etc. it seemed a cold statement but we thought he was just happy to be stable. Kindergarten comes and her in and out attitude continued. She wanted absolutely nothing to do with his school life for a while. Then it all changed. For her spring break visitation she went nuts and refused to bring him back. We ended up having to get lawyers. Then she filed a restraining order to try to keep him however this didn't work and she had to return him. This is when it all went really bad and she must have had some psychotic break or slipped in to some intense mania. This is when the court gave her supervised visitation due to the things she said and did during this time. She never used her visits. When we went to court they gave her every weekend and everyone was disturbered. They said she had to get mental help etc (which she never did). Every weekend he went there got worse than the weekend prior. He would go over there and say awful lies about us to make her happy. We previous thought this was her pushing him to say these things but we see now that it was him egging this on. The bm called cps. We were investigated and had to let this lady invade our home. We were relieved to find ss told the truth about us to cps and the police and they closed the investigation and cleared us. Since then ss lies have gotten worse. He claimed he loved his life and his school and living with us. We told him it is important he stop lying to his mom and that if people come to talk to him that he needs to continue to tell the truth if he wants to keep living with us and going to his school etc. fast forward to the weekend before thanksgiving (1st grade now). We go to the exchange on Sunday and she isn't there. We got an email from bm saying she won't be contacting us again. We spent 3 days trying to get him back. Cops called over there and ss says he doesn't want to come with us or speak to us. Bm indicates that cps has opened a new investigation based on abuse. So now the cops really won't help. We finally arranged with a Sargent to go pick him up. We spoke with the cps lady who said ss made abuse allegations against us this time. (All lies we can't believe this). He says he wants to stay with his mom. He lied to cps to stay there. Now we are being investigated again!!!! Meanwhile I will note cops keep showing up to our house to "investigate" my husband goes to speak with his son when we were picking him up. My husband and I thought he was pushed to make up allegations from bm and did want to come home but was too scared to say in front of bm. Ss tells my husband he doesn't want to come home and that he is okay never going back to his school or seeing his friends again. (Not normal) my husband says he didn't have to lie about abuse and ss says "well one time we were playing and it kinda hurt my arm a little". We are disturbed by recent behaviors we have been dealing before this as well. Trying to hurt me etc. ss does see a therapist. This has gotten to a point where we feel our safety is compromised. We keep having cops show up we are being investigated by cps all bc he wants to go back to his moms. We understand a 7 year old doesn't get to decide where he lives. Cps seems to be on bm side and won't believe her home isn't good for him. At this point we feel that he can't stay here either. If he stays we will be walking on eggshells and will worry that he will be lying to authority about us when he doesn't get his way. I don't want to see him ever again and my husband is slowly feeling the same way. We are devastated and don't know what to do! Please help with any advice we are so sad and lost.