I don't get guys.. what does this mean?

I was more or less seeing this guy from the end of last year until after I caught him sending let's say 'intimate' images to another girl, before this incident he was sweet, lovely, cheeky and always complimentary.I overlooked the whole picture sending thing, and we started talking again but he's just so different with me, he makes me feel like I mean nothing to him and constantly ignores me if we're not on the subject of something about him, I've got to the stage where I just don't know what to do? I don't want to lose him but I don't want to continue feeling like this..