Don Draper doesn't need to pay for sex. He's the dashing and distant man that brown-haired women can't resist. But last night, a prostitute strode into his apartment and smacked him around.
Is this another case of a high-powered executive needing his career-driven ego slapped away so he can surrender to fornication's id? His need to be dominated is new, suggesting that it stems from his recent divorce. His untenable identity was given a pillar of stability as husband. But without the ring on his finger, he's thrown into confusion. In the opening scene he's asked, 'Who is Don Draper?" and he can no longer fabricate his stolen identity. The shackles of marriage are off and he's unable to cope with his new-found freedom. Camille Paglia theorizes that 'whenever sexual freedom is sought or achieved, sadomasochism will not be far behind.' He's found a new way to enslave himself through a bit of hanky spanky.
Not to be overlooked is his Oedipal return to the mother figure. Don the whore-child escapes the confines of wife only to bring a prostitute to his bed. Projected in his work, his heralded Glo Coat floor cleaner commercial shows a little boy literally imprisoned by his housewife mother. In an earlier scene, he goes on a date with a Betty-type rules-girl. He is the constant prisoner of women... will he ever resolve his Madonna-whore conflict?
Professionally, he embraces the burgeoning sexual liberation of the 1960s. However, the clients, stuck in the priggish 1950s, are disappointed because the image isn't 'wholesome.' They even attempt to desexualize the bikini by calling it a two-piece bathing suit. Understanding the power of innuendo, Don cuts through their conflicting agenda by pointing out that his suggestive advertisement is a way to get your clientele into the store. As a customer of sex, Don knows its selling power. 
Elsewhere in SCDP, Peggy conceives of a guerrilla marketing performance to sell ham. She hires two actresses to stage a fight over her client's brand of the pink meat. Only this staged aggression makes the easy leap to reality and one of the actresses lands in jail from assault charges. Like sex, aggression and violence are difficult fires to control.
Ex-wife Betty is certainly taking her ugly pills. She's become a monster of a mother to Sally, the little blonde girl able to sustain Don's devotion and love. In a genius scene, Betty transforms nurture into violence when she shoves sweet potatoes into Sally's mouth, humiliating her and making her gag at the Thanksgiving table. Jealousy is the driving force here -- Sally is the little girl that Betty wants to be, unconditionally loved by Don. The poor thing just endured her parents' divorce and now she's living with a frigid and unloving mother. I used to pity Betty as it seemed that her marriage to Don made her miserable. Alas, misery's the river of her world.
From the bedroom to that blue Cadillac Coupe de Ville that Don purchased in Season 2, Henry Francis is having a field day rubbing his scent all over Don's house and ex-wife. Bent on erasing Betty's ex, he's so whipped he refuses to see Betty's belittling treatment towards her daughter. As his mother said, "I know what you see in her, and you could've gotten it without marrying."
So common in divorce, Betty is using the children as passive aggressive vengeance on Don. Cunningly, she gives baby Gene to Carla before Don has a chance to see him. She purposely returns home late from her date with her new husband, all the while knowing that Don is forced to wait in his house he no longer inhabits. At first emasculated by new Daddy and spiteful Mommy, Don finally asserts himself and tells them to leave the house or start paying rent. When asked again, 'Who is Don Draper?' he's able to define himself. Betty's behavior was the final slap in the face he needed.