Brainwashed...what should i do?

My partner is being brain washed most likely by his sister and she is doing it slowly and cleverly, he used to adore me, we know each other for 15yrs and since past 1 yr he has begun to dislike me, he doubts all my actions as though I am plotting things against him, he will one day apologise for his actions and say he doesnt know wht got into him and then the next day he will loose temper and begin to dislike me again. He doesnt trust me one bit and over the yrs i have sacrificed so much for him for which he adored me, he now has forgotten all tht and no matter how much I do for him now, he takes it negatively and comes up with weird umptions which in turn make me loose my temper and he begins to dislike me even more. i was left stunned when it all began to happen since 1 yr, only now I have reached the conclusion tht his sister is doing this to him an she is doing pretty good job cos we cud be divorced pretty soon. I dont know wt to do