What are the rules of ending a rental agreement early when flatting
Background:
-Partner and I moved out of our old rental and started flatting with partners cousin and cousins girlfriend.
-We are all listed as tenants on fixed rental agreement.
-Since we've moved in I've had a problem with living with cousins girlfriend. Leaves her mess around, doesn't clean shared space, does bugger all when inspection week comes around and partner and I scramble to get house decent for inspections.
-Been over it since day one, however due to cousins work situation I felt bad and agreed I'll stay and signed for another year. Despite not being happy and feeling trapped in current living situation.
-Rental agreement ends March next year.
The last straw:
-Found out cousin and cousins partner has bought a house on Facebook marketplace as I saw them advertising rooms for rent that wasn't a house I've seen before and asked about it.
-They get keys to their new home next month.
*Note: they didnt tell us they had intentions of buying, otherwise I wouldn't have agreed to extending current rental agreement.
-We knew nothing until I randomly came across post on marketplace...
Advice needed:
-What happens if I want to leave the current rental as I am also on the tenancy?
-Can cousin and cousins partner object?
- Cousin told me they will stay till next March in current place, however my trust is gone and for the sake of my mental health Id rather not take their word, wait around and find out. Id rather pay whatever the landlord wants to break the agreement and leave.
-Ive started looking at places already. What would happen if I was to move out next week?
-Can me wanting to leave be brought up with property manager without them telling cousin?
What are the rules in this situation?
Any advice would be greatly appreciated.