Don't laugh

I don't know where else to go to ask these. These questions were raised due to new experiences with a cheating partner, so I seek advice.
I've heard several times that anal sex can make the receiver feel like they need to poop after. Is this sensation caused by the insertion or the ejaculate inside?
If a girl claims their partner bent them over after some passionate foreplay and fully pushed in (a six inch dick) about eight times before the receiver realized they were in the wrong hole, is that a believable story? I would think it would be clear the penis is in the wrong hole after the first full insertion when bent over.
Would a girl (who love anal sex) avoid sharing their love for it with new partners and love interests for fear it makes them look dirty?