I need advise regarding an issue with my husband.?

He always tells me he has my back and will stand with me instead of against me. Recently though I've found that what he tells me to my face and what his actions do are two different things. I've overheard him bad mouthing me to his family and even my sister. Little things like saying to his cousin on the morning of fathers day that he didn't expect much from me. (i always go all out for him) or he will tell my sister things like don't tell her i said this cause the wife will get all mad. he has talked a lot of **** about me to his mom in the past every time we fought he would run to her and tell her everything. go figure now the woman hates me. i have confronted him about this and he said he understood how i felt and wouldnt do it again. but he is at it again! if for example my sister and i are fighting i notice a more often approach to him being friendly with her. it's almost like he wants me to see that. he just says he plays stupid and doesn't ever want to be in the middle. that i do understand. but what i dont understand is when he says he has my back but he never does. his family always bad mouths me and he has hardly ever stuck up for me. he always tells me he would, but when it comes down to it i'm standing on my own. if we would say nice things about me or tell the truth once in a while, maybe then they wouldn't see me in such a bad light. it hurts real bad. also, i might open up to him and tell him stuff, confide in him. later on when we are fighting he will use it against me. i don't trust him like i used to, more so i[m hurt. any suggestions?