lies and eyes for other women

My SO of a little over two years lies to me about dumb shit. And it literally irritates the shit outta me. Recently I was scrolling through Facebook and seen that he had followed some girl who's profile pic was her in lacy underwear and a Tank. I screenshotted it and sent it to him the next morning. And when I asked him why he followed her, he told me that the comments on her profile were hilarious (she's kinda rough looking possible drug addict and posts dancing videos). But when I looked at the comments I didn't find anything funny. BIG FAT LIE! I told him that I know why he followed her and asked him why he seeks out other women. And by seek I mean following, looking at, PORN, etc. I know it sounds silly to be mad at him for just simply following someone but with her posts half naked and provocative dances, I feel as if it's wrong. Another time I found out he was talking to an old sexual partner on snapchat. He said they were just friends but when I asked him if they had sex previously, he said yes. I felt so hurt and stupid. How could I be so oblivious? He deleted her off of snapchat but made it seem like what he did wasn't that big of a deal. I explained to him that it was a big deal to me. But sometimes, especially lately, I feel as if he's not sorry. If he was I wouldnt have to tell him that talking and seeking out other girls is inappropriate. When we first started dating he had a big problem with porn and masturbating. I would ask him if he masturbated and he would lie and tell me no. I knew he was lying by the loom on his face and he would confess that he did. He just lies about little dumb shit. Like the other day he was super hard for awhile while we were kissing and stuff and I was suprised by it. Low and behold he took a viagra. Which I'm more than okay with. But he lied and said he didn't know why he was so hard. It's not so much what he lies about (except for the women) but more the lying that bothers me than anything. And now I feel like he's just being sneaky with me. And I don't know how to make that feeling go away. It sucks. Idk what to do. How do I trust him after all the lies and the issue with "having eyes" for other women?