Vlado said:
It feels like a big deal until you actually have it, and then you realise it really isn't.
Or if you haven't had it for a while. It can vary from person to person. I'd say about half of it is mental, and the other half is HEAVILY dependent on biology.
As for the O.P's post, I'm going to echo the others here. You should really find a way to just talk about it. I know there are emotions on your side-- the feeling of being withheld from or rejected. Just realize that she's not *trying* to hurt you, and it's not about you to begin with.
There is, of course, the possibility that she may be defensive about it. There's only so much you can do to help with this. Just be frank, and reasonable in how you talk about it with her. Try not to make a big deal of the discussion, avoid pressuring for an answer, and just be willing to listen.
Above all, make sure your heart is in the right place. You need to approach this not as a goal or a problem, but an open-ended question. Approach it as a guy who just wants to understand her frame of mind better, because then you can be better to her as a significant other.
The great thing about this is that if she's willing to talk, and if you do well in being positive and receptive, you'll have made communication better overall which can pay huge dividends in any long term relationship
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On another note, saying "Sex isn't an absolute need", while technically true, risks vastly oversimplifying the matter.
It's like how we have an innate desire to improve our lives. Learning, building better houses, making our food taste good, socializing, all these are not "technically" needs, but we have an inherent drive to do these things. Besides which, our lives would be utterly devoid of color without them.
So, do we chide those who "make a big deal" about paying a predatory mortgage loan because they could have just found a secluded wooded area and pitched a tent? Do we berate those who "seem to have a hang up" with eating more than wild kale, fish and fruit and for drinking more than water? Or do we grant that these things, while not necessities, play a huge role in fulfilling the drive to do more than just survive on the bare minimum?
And that, like sex, is a drive that does not leave the vast majority of us alone. Ever. It's with us constantly, compelling us to do this, go here, do that.
So it is with the desire to actually physically have sex and seek a connection. This may or may not coincide with the notion of Love. To each their own. {Though there are those whose self-righteousness compels them to judge others for that.)
<./rant>
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(EDIT: Premature post. Make of that what ever you will.)