I'm not sure where else to post this so sorry if this is wrong, just in need of some pretty quick advice.
My DH and I are in the very early process of separating - we agreed last night that he will move back to his mum's this week. Things have been difficult for ages and we went through a lot of stress last year when he lost his job. I took out a loan to see us through, but he found a new job after a few months. However he found out on Friday that he had not passed his probation. This has tipped us over the edge - we spent the weekend arguing and it's not good for my DS. I don't believe he tried hard enough at the new job or took on feedback from his previous employer about his negative attitude.
I work full time but three days a week I leave very very early in the morning whilst DS is still asleep. DH then gets him ready for childcare. I absolutely cannot change my working hours, and DH cannot have DS at his mum's (her house is not appropriate for him; stinks of smoke, no room for a bed, and we only adopted him a year ago and neither of us want to disrupt his little life that is relatively settled for now.
Our plan is that one night a week DS will sleep at my mums and she will get him ready in the morning (he has sleepovers there all the time so this won't phase him), and the other two mornings a week DH will stay over that night to get up with DS I will stay at my mums these nights or he will sleep on the sofa.
I'm worried that if I apply for universal credit (which will be about £80 a week, which I will need to survive!) He could still be seen to be living here if he is staying here two nights a week. Is there anything we need to do to formally declare that we have separated (we don't know yet if this is temporary or we will look to divorce, but divorce is definitely looking likely). I'm so stressed I don't know what to do. I can't see another way around it and I can't give up my job.