Just need to Vent :(

I feel like I am a pretty cool partner to my SO. I don't nag, don't ask for much, make money and help support him and his two kids (one lives with us full time). I don't bother him much, but I do ask for honesty and respect 100%. We have had a few instances where I have caught him lying... Mainly about porn. Generally it doesn't bother me except he took it a step further a few years ago and... Let's just say he made some bad decisions (no cheating but was very dishonest). I said since he broke my trust, if I am not putting out I would just ask that he is respectful and honest if he is watching porn. Sure enough on Saturday I grab his phone since mine was broken and opened the Internet, he left the private webpage up with porn. Wasn't even mad yet, went downstairs and asked him if he would like to fess up. Lied... Lied.... Lied. Then I get mad, thinking do you think I'm dumb? And I'm pregnant... I am already so self conscious yet willing to have sex whenever and he waits for me to leave to watch porn and jerk off? What made me even more mad was when I wanted to talk it out he shut down and then was mean to me. Ladies we know what defensive means... He's hiding something. I just felt it... But I'm also hormonal. I know there is a lot to the story, but after having the same fight over and over, going to counseling, trying so many things... He just can't be honest and I don't know what to do :( Guess I am just looking for thoughts, advice. Once a liar always a liar? I always have fear in the back of my mind that he's hiding something. Is this  normal? Thanks for listening!