Because there are other forces at play which were pushing him away from you.
These "rejection" forces happen to be stronger than the "attraction" forces.
Look at it like a combination of forces.
If you didn't find the answer yet, there is obsviously some resistance or rejection force you still did overlook or not identify.
Again, the answer is probably in one of the possibilities I mentioned earlier:
- Material needs
- Social status
- Cultural background
- Family approval
- Too much intensity
- Personal background
- Career line
All these potential sources of objection can play a significant role when he decides to break up with you.