How to move on when..

They left you so abruptly, I was dating this guy for 4 months.. it was going great, HE was the one telling me “I love you” HE was the one suggesting to meet his family, HE was the one talking about our future. I was more cautious & one day he told me he couldn’t continue with me anymore, I’m so torn & confused.. & his reason was maybe we’re on different pages. What???? He knows we were always on the same page, then he changed it to we argue a lot.. no we haven’t. The last time we had a disagreement was two weeks ago but it’s nothing more than a disagreement. I’m so confused & mad because my gut feeling is telling me he’s not being honest with me. How do you move on when you don’t even know what happened? All I do is think about what went wrong.. no help because I have no idea why he ended things