Am i soley responsible for all the rent even tho they ALLOWED my leasemate top leave and he is still on lease?

So heres the long story, i have a year lease with a...ex boyfriend..we moved in alond with a child and a dog (big pitt, landlord was fine with it) now we had got a second dog (puppy pitt) and the lanlord said we had to get rid of the puppy. my ex boyfriend ended up moving out with his big dog, but his name is still on the lease, and in the process of him moving out the lanlord evicted us for having the second dog. when he left my puppy was left in subsitute of his big dog, but they still wanted to proceed with the eviction although rent was always paid n never any disturbances. now..my ex is still on the lease and letters from the lanlord who resides upstairs from us still address eviction notices or any letters to tthe both of us. lanlords knew we went 50/50 on rent but let him leave. do i still have top pay the entire rent even tho he is still on the lease? they havent taken him off the lease and last month i used my sec deposit to cover rent since my lease mate left me high and dry, and they tried convincing me to only give my half of the rent. this month they are saying i have to give it ih full. what do i do? wut are my rights?