Living with a partner

Hello, I am chronically ill and disabled. I have been deemed LCWRA and I also receive PIP. I moved in with my boyfriend last year because I couldn’t cope living by myself. Now my boyfriend works full time earning around £2000 a month depending on overtime and night shifts. I was getting some pay from work (long term sick leave) but in August that will end and I will be fired. This will mean that I will have to survive just on UC. I have worked out that if my boyfriend earns £2000 a month, the universal credit amount will be only £930 for me. If I was claiming as a single person it would be £1300. How is this fair? My boyfriend and I split everything 50/50. I pay half of everything. I have spoken to him about him maybe paying a bit more than half but he is refusing. I have no access to his earnings. He does not support me financially. We do not share bank accounts. We don’t even share a bedroom. If he earns an extra £200 in a month, that £200 will be taken away from me. I don’t know what to do.