Jeeeez.....
So their solution is basically to tell her you want it & then stick your finger in her ass when she's about to cum ?
Sorry - but I'm not in touch with my feminine side whatsoever, so let's dispense with the gradual/caring/sharing approach. Here's the deal. I've fucked a number of women up the ass who never had anal before and ALL of them have thanked me afterwards without exception.
There is just one rule when it comes to anal. They just have to commit to trying it twice, not once.
First time, they are going to be waaay to nervouse and uptight about it.
Second time, they will be more relaxed, as long as you have spent some oral time on the clit & some dick time on the pussy beforehand, it's going to be like putting a warm knife through butter. If she doesn't cum through anal sex on your second attempt, then you really need to work on your self control. Two pumps and a squirt is not going to get you a re-match.
