With-holding of sex is a classic Passive Aggressive behavior.

“Abstinence is a common complaint from women involved with passive aggressive men. If he’s in a financial pinch, he’ll take you out for the evening but remind you that the evening’s expenses are a huge burden. He’ll then make up pay by refusing to have sex. But if you offer to go Dutch before he suggests it, he’ll take it as an emasculating gesture. And still he’ll make you pay by withholding sex. His sexual refusal, however, will usually be hidden under the guise of a transparent excuse: he’s sleepy, sick, preoccupied with work.”

The Passive Aggressive 'often uses outright sexual refusal as his/her main weapon in their battle against you'. 'Abstinence comes easily to someone for whom sex is not about giving and intimacy but about proving something to his/her-self'. 'Its a replay of the frustration and deprivation of childhood', if he/she upsets you and makes you question your attractiveness your own sexuality your own self worth he/she has carried out the PAs perfect crime of omission. He literally has done nothing

Because the PA does not make an emotional attachment I think they still go for a visual attraction, so if you put on weight etc they will use that ad ab excuse. Could come across as abit shallow and narcissistic.

They will project back onto you: when I finally called my W on this she projected back onto me 'I am trying to work out when YOU started having a problem with sex."

Telling you how great sex was with the other person is just designed to punish you further ignore it, it is just total BS.