"He desperately needs to keep Homs open," says Dan Layman, head of media relations for the Syrian Support Group. "Qusair is a big, big deal."
The regime has regained control of roughly 60 percent of the town, putting a strangle hold on supplies and additional manpower for the rebel fighters. Assad, too, likely sees this as a lifeline.
"He sees the writing on the wall that things are going badly for him, so he'll be drastically changing in the next six months," Layman says, adding that it will be very difficult to regain control if Qusair falls to Assad. "If Qusair is taken back by the regime, it's going to be a huge morale blow [for the opposition]."
The regime's recent success in and around Qusair and Homs is due largely to support from Iran, Russia and Hezbollah, according to private security firm Stratfor.
"Hezbollah has long been involved in the fight over Homs, but the May 19 offensive marks a clear escalation in Hezbollah's involvement," it says in a report released Monday. "Tensions in Lebanon have grown alongside this increased involvement. For example, rebels struck the Lebanese town of Hermel with rocket artillery on May 19. And the anger Lebanese Sunnis feel toward Hezbollah threatens to spill over into a full-blown armed conflict."
Iran and Russia also continue to deliver much-needed supplies to the Assad regime, including supplies for its air force which it uses to deploy cluster bombs and other ordnance against the rebels.
"External help also enabled Syria to create a new militia, known as the National Defense Force, to offset the losses incurred by the army," Stratfor says. "With the help of Iranian and Hezbollah advisers, the regime was able to rapidly train and deploy members of this militia."
"Over the past few months, fighting has regressed to battles of exhaustion and campaigns of attrition," Stratfor adds. "Instances where the rebels could quickly seize a major city in only a few days -- as they did in Raqqa -- are the exception rather than the norm."