Blanche's marriage was a love-match to a man with a marvelous voice (played by George Grizzard). In the years since he died in a car accident, she has dated man after man. Although she has a reputation for being "loose," she is far more discerning and careful than she presents herself.
Rather like Dean, who scorns God because he feels threatened by his own disillusionment, Blanche treats relationships as fleeting because at heart she wants another "one and only" relationship.
Only, when she actually does get close to the altar, she ends up with duds. The one non-dud (see Season 2), she dumps.
Arguably, Blanche knows she can never have what she had with her first husband. So she sabotages herself. The pursuit of romance is her coping mechanism.
And hey, that pursuit provides a continual string of plot points!
