Unconditional love does not expect anything and therefore immune to "heart broken- ness". You break your heart because you expected something. The first is outward bound, and like an oasis, it will never dry up.
The other is not exactly the opposite. It is quite normal. However, as any relationship, no matter how casual it is is a divine contract, then one must move on knowing that whatever the outcome was, it was the best that could happen at that moment in time. One must not blame oneself or the other.