TL;dr - If you're not feeling passion for a woman, you might not be feeling passion for your life's purpose. Find and pursue the latter, and the former will come (but be selective).
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I'm going to take a slightly different tack in my answer and ask - besides wanting to feel more passion to fuck women, what ARE you passionate about in YOUR life?
If you don't have something you really enjoy doing, are working toward mastering, that is making you a better man and earning a place in the world, you may not feel motivated to do much fucking. Your time and energy is spent just doing whatever day-to-day, falling into a routine, being part of someone else's plan:
"If you don't have a plan, you become part of someone else's plan." - is a quote I always keep in mind
A self-made man has a plan, is neither slave nor fool. Just being horny enough to fuck a woman can peter out once you're out of your teens and early/mid-20s. Eventually, ideas of life purpose and meaning start to take center stage. What is your campaign? as Roosh asks?
http://www.rooshv.com/what-is-your-campaign
I suggest that you get clearer on what your life is about (see my posts on 'finding your genius / life purpose', also check out David Deida's videos on Youtube, and his book 'Way of the Superior Man'). Spend some time by yourself, journal, meditate, walk, be in nature, and then talk with men you can trust whether family, friends, co-workers, or a cool bartender. When you focus time and energy on your goals, you're going to exude an energy that will draw women in. It's up to you to select for higher quality women as fucking any random one (i.e. a woman who doesn't have anything of value to contribute to your life) will drain your essence and vitality. I've been there, done that in my late 20's/early 30s. A lower quality woman is a sure-fire way to fuck your life up and you're getting to a point whether it's clearly not about just getting laid, but finding deeper meaning (at least I'm assuming that's a motivation).
I'll co-sign on (organic) Maca powder, the stuff is amazing. I also take 30 mg of L-Optizinc during lunch, typically eat about 4-6 raw eggs, ZMA (zinc magnesium vitamin 6) before bed, about 3,000 iu vit D3, ~400 mcg selenium, quality male multi-vitamin, etc. I'm BURNING with passion for what I'm creating in my life and when I look for a woman I'm selecting for those who dig me and my mission.
Desire for its own sake is fun but fleeting (hey, we all go through it!). Passion grows as a result of respect and admiration for your victories and is in a whole other league of intensity. As the saying also goes, 'most men lead lives of quiet desperation.' Don't be one of those men - stoke your fire, heat the iron of your purpose, and shape it by your sheer will and commitment into the life you want to create. You're here, we're your brothers, and we want you to succeed in your mission.
Your passion sustains and builds as long as you keep being a man of Quality, worth a woman's trust and desire. Sometimes, I can see a palpable shift in a woman's eyes when I'm sharing my story, my vision, and where I'm going. I don't depend on their desire, but it's nearly impossible for me to want to fuck a woman (at least more than once) if she doesn't get me at a deeper level. She is opening herself to me, in trust and from a truly feminine place that I've earned by being a man who deserves to open her. This is a power that you also need to respect, because breaking hearts is bad karma (had to learn that lesson a few times too).
