Hezbollah is a large millitant group mostly based in southern Lebanon with a goal to resist Israel.
It had large popular backing when until around 2000, Israel had occupied southern Lebanon. It got a lot of support from the people on the street, and the governments of Syria and Iran.
It has also been involved in two conflicts with Israel since the Israeli withdrawal, but still enjoyed widespread support as "Legitimate resistance" and also for being a thorn in Israel's side.
The people of Syria supported Hezbollah almost totally, and this was helped by the fact that the regime also supported Hezbollah as its trump card to hit Israel should any hostilities arise with Israel or its allies.
The people of Syria gave them shelter and support.
In return when the people of Syria at the start of the Arab spring rose against Bashar Al-Assad were surprised to find that Hezbollah did not support them.
However this was not a total surprise as both the govenment and the people of Syria had supported Hezbollah, so Hezbollah not getting totally involved on one side or other would be expected.
But now, Hezbollah has openly opened a front against the people and its fighters are openly fighting on the side of Bashar Al Assad and his forces, and are fully complicit in the policy of intimidation and murder.
It has betrayed the people that supported it through great cost to them.