Habit, is this something to be mad about?

My fiance' now and I have been together for four years, we also have a three year old daughter together, he's also being deployed to Kuwait for a year. Lately we've been having a lot of issues with lying and . It started out with him looking at it, he used to be really bad about it and then apparently 'quit' it came up a few times over the course of a few weeks and he would continue to 'swear to god' and 'swear on my life' and promise me over and over again that he wasn't doing it. One night I was online on his phone, and had pulled up the history to find a page that I was on and write down the link, I find ..a lot of it..I called him out on it the next day and we had a long discussion on how this hurt my feelings and that I was really hurt that he would swear on my life and lie to me for weeks, he agreed he wouldn't do it. Last night I was on his phone again and I clicked on the Google search bar..When I clicked on it, 'xvideos' came up, I waited for him to come upstairs and I asked him if he was looking at it again, he told me 'no' and continued to try and backtrack..he told me it was from a long time ago and once he knew he couldn't get out of it he admitted it..again, he had been lying to me since the last time I found out. I explained to him that I wasn't upset about the as much as I was that he lied and lied for weeks, he swore on my life and tried to make it seem as believable as possible. I'm wanting to know..Is this something that I should be genuinely upset about? What should I do? Should I let it go or?? Thank you to anyone who can help!