Since Brenda was not actually in love with Jax, when she and Sonny got stuck together while kidnapped by Sonny's turncoat bodyguard, the pair made love. When Jax found out, he left Brenda, and she and Sonny were finally free to marry. 

Of course, it wasn't meant to be — this time around. Brenda arrived at the church ready to walk down the aisle, but Sonny wasn't there. Instead, in order to protect her, he quietly left town after threats were made on his and Brenda's lives.

When Sonny returned to town nearly two years later, Brenda had been presumed dead in a car crash, and Sonny had to learn to live without her. 

However, Brenda wasn't dead after all, and, when Sonny saw her alive for the first time outside a church with "Amazing Grace" playing in the background, it was a cathartic moment for them and the audience as they finally reunited. 

But not for long. Jax also fought for Brenda, and all the chaos prompted her to leave town once again.