Helpppp Stepdad&Mon

I’m 15 & I have a sister who’s 16. Stepdad,Mom,sis & I used to live all together then we moved to a different place which is with my step grandma. All that work from moving and now my stepdad & mom are breaking up. I feel sad. My stepdad has done so much for us. Especially my Mom but she just really has trust issues or she is saying there’s this gut feeling in her that tells her that he’s doing something not good like cheating. I honestly don’t know what to do. I just want everything to go back the way it was. I was really happy but I’m also worried about my mother she’s probably depressed. :(