I imagine that there are lots of men who would envy your dilemma, but I don't mean to belittle it (so to speak). Have you thought about using some toys? Perhaps getting a nice big dildo would take some of the pressure off you, or at least give you a few days' rest in between bang sessions. You could also ask her what exactly it is about the "hardness" of your intercourse that she enjoys. Is it the violent aspect? The intravaginal sensation? The feeling of her pubic bones cracking against yours? Once you deconstruct the problem, you might be able to find an alternate solution. Good luck, and -- oh, cripes, I gotta say it -- may the force be with you...

It's usually a sensitivity issue unless she gets of on the hard banging in which case it falls under fetish. First you'll be glad to know there is a middle ground , but you'll need time to get to it...
You'll need to pick up the pacegradually and don't worry, you're body will acclimatize to the impact and the soreness will soon disappear, and with the use of toys you can get her used to slightly slower pace, which I'm told she'll savor all the more...
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I would stay away from using big toys or things that hammer her since this will only aggravate her sensitivity issue...
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Of course all this requires an investment in each other, and so you'll need to determine if it is worth it for both of you. ..
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-Carlos..
Angie's my hammer...