Sue Ellen behaved very selfishly by leaving Southfork whilst JR, Bobby & Ray were in South America.
All she thought about was herself.
She didn't stop to think of the consequences of her leaving would do to the Ewing family, not just JR.
Sue Ellen was a part of the Ewing family and she chose to ignore that by leaving Southfork whilst her ex-husband & his brothers were searching for her Father-in-law, the founder of Ewing Oil - Jock Ewing.
I never understood her explanation that all she could see of JR's return from South America without Jock was a hurt, little boy.
Sue Ellen had the opportunity to support Miss Ellie & the Ewing family & help them cope with the death of Jock but instead chose to abandon them for selfish reason's of her own. I was not impressed with her then & I'm not impressed with her now.
At least Pam was there for both Bobby & Miss Ellie. Pam showed her compassion for her family & her husband & indeed for Jock too, especially as they didn't always see eye to eye. Even Donna stood by Miss Ellie, Ray & the family too. Sue Ellen was a different story she just couldn't wait to leave. She couldn't cope with the possibility of leaving JR if Jock was dead so what did she do, she scarpered.