should I take him seriously?

So my fiancé & I have managed to stay together, even through all the fights & bull shit... But a couple months ago, a few weeks before my birthday, he told me he wasn't in love with me anymore... & that he wanted me to move out, because he wanted to be alone. As I was getting ready to leave, he begged me to stay, told me he was sorry for saying all the things he said to me, & that he didn't mean to hurt me... So I stayed, because I do love this man with all of my heart. He promised he wouldn't say hurtful things anymore, promised that he wouldn't get online anymore to look up girls on Craigslist or watch porn behind my back, or other things he was hiding.. Well last week, I caught him on Craigslist again, & I didn't start a fight or anything... But I did ask him why he lies & does these things to me? Even with me having sex with him constantly, giving him bj's when he wanted them, even jacking him off right before bed. Like he had no excuse to be "horny!!" He was telling me that he didn't know why, & that he didn't care how I felt about it, that he just wants to be alone, & left for work. When he got home I was crying because I was still hurt. & he came up to me & apologized for everything. Said he didn't know why he woke up in a pissed off mood, & he took it out on me & it wasn't right of him to do... & as far as the craigslist & porn, he had no explanation or excuse. He was just being a pig. Of course I forgave him, & things have been a little different & better.. But we were outside talking today while we smoked, & he just asked me if I wanted to get married as soon as we get our taxes back. Not a huge wedding, but at the courthouse for now. I told him I wasn't sure, cuz of everything that's happened, & been going on. He said he was over being that person, & he realizes how special I am to him, & he wants to make me his forever... I just dunno if I should believe him?? We've been through way more than just this.. & I'm just afraid he'll use marriage against me, if we ever get into a huge argument again. Or if he only wants to marry me, because I'm dumb enough to keep forgiving him? What should I do? He picked out this ring for me, says he wants me to be his wife forever.