Perfect to heartbroken

I have a question?

Me and my boyfriend have been together for 4 years. Weve had our ups and downs but recently our relationship has been perfect! Weve both said it. Weve become a lot stronger and happier together. A couple of weeks ago he asked me to come round and stay but I had work the next day and it was already late? The day after he ended things saying he had things going on and he doesnt want a relationship.

I dont understand how you can be happy and things be good to ending the relationship the day after? I need your guys thoughts on this? Please help because I am really struggling to understand this right now. How can you change your mind overnight so drastically????