Break-up out of nowhere!

So i've been with my boyfriend over 5 months and we had a lovely relationship. We had our arguments etc but we always sorted everything out in the end. because i was from another country i decided to go home for summer, for 8 weeks after my uni finished. At first he was a bit disappointed that i was going but i told him 8 weeks will fly by. Last few days before i went home he couldn't stop calling me or texting me saying he feels like crying cos he misses me that much, he told me to text him all the time while away and call him. He told me how much he loved me and missed me every day, he even cried once saying his heart hurts when thinking about me because he feels so depressed without me he can't stop thinking about it. So two weeks into me being back home he didn't text me all day and then when i asked what was wrong he said he can't be bothered with this anymore and that he loves me but had a change of heart and we shouldn't be together anymore! Like whatttt?????? what the hell happened? I was just in shock and i feel completely stressed out because i keep thinking of all the nice things we did and said and planned for the future and now this....

He probably found another girl while you were away.

I don't think excellent relationships end for no apparent reason. So there must have been a reason. What was it?