What do I do!? Husband is secretative and lies to me about silly stuff!?

We have been married for 10 years, He has always like to watch porn , but recently he has been on SEVERAL adult dating sites some say couple looking for.. etc and some say single man looking for etc... I tried to talk to him about this but he blows it off like it is no big deal but then past 2 weeks he has changed the password to an email that we set up together and the pass code to his new Iphone that he is on 24/7 recent issue was my b-day my mom and sister and the kids did the whole cake and candles because the past 3 b-days have SUCKED he did not even come out of the bed room all day was on the computer and only came out late afternoon and got on the phone with his parents and then spoke to his sister until late that night oh and it was also Father's day! which brings me to my sister in law ... we were great up until 2 years ago his family lives out of state in FL wanted us to move there but it was not the right time for us to move she blamed me and on our last trip there gave me the cold shoulder the entire time which made my husband do the same I noticed the last few days they were whispering a lot more but I didn't pay them any attention but found out why on the Long drive home! Half way home still had 6 hours to go my husband unleashed a horrific fury on me calling me a thief liar pathetic it was catastrophic with the kids in the car accused me of stealing his 12yr old niece's perfume.... He allowed his sister to go through my purse and remove a bottle of perfume that MY SISTER had gotten me on my b-day. needless to say they found his niece's bottle under her bed wrapped in a towel .. my husband not one time took up for me ... or even really apologized for not standing by me!!! He has 2 kids from a previous marriage and we have 2 boys together my sister in law flew the other 2 kids to FL last year without even thinking of these boys.. I was furious because my oldest was very upset then christmas she sent the other 2 a present to our house not the boys one when I politely told her to please from on send packages to their mom's house she went off on me in text calling me all kinds of things and said that they were mixed up she sent them all at the same time but on the package the date was 4 days after our conversation. Now she has done it again the other 2 are in FL now with her and my kids do not know yet we didn't know last year till the post of facebook! When I try to talk to him about his sister and MY issues with her he gets ballistic puffs up like a blow fish and defends her every action and doesn't even listen to me we don't speak for a while then he acts like nothing happen! Well I am sick and tired of all of this I don't know what to do am I overreacting or what can I do ... he doesn't take up for me at ll I don't feel like he has my back at all!!! HELP ME