But you're discussing a cause and effect in an objective sense, which means that you're potentially above the notion in the first place and able to navigate the issue. Encase it, and treat this in itself as an objective problem. That's what a scientist would do. What you need is a sound method, and an improvement in your own semantics and symbolism.
Take "mental stability". Would you mean that when you lean to the coldly rational mindset, you behave in a dysfunctional manner, as you see it?
If things doesn't mean anything - then so what? And in light of that, what's the normality that you're swinging away from? What's the meaning of you describing yourself as having some kind of mental pivotpoint? That's not an actual thing, it's just a metaphor for transgressing the boundary of a meaning or value of yours. What are you actually talking about? This isn't like an aggressive challenge from me to you, it's how I'd talk to myself in this situation and I think it is a useful way of breaking down the semantics at the heart the problem - how you conceptualize your outlook.
Actual Nihilism is not a negative philosophy, per se, to me. It gives you a platform to analyse the meaning of your actions to yourself. It doesn't prescribe a model behaviour - a person can swing either way from the nihilist position in polar directions, and even e.g.choose to be a fully functioning good Christian, even though they scoffed philosophically at any sort of mystical idea. So what, if it appears contradictory to people who are immutable from a mindset that you've already decided makes no sense to you? Their perspective isn't valuable to you, nor yours them; let God make sense to them, extract the goodness in Christian virtue for yourself. One wouldn't even have to go out and say "what you are", you don't have to brand yourself.
Just enact it, and be objective about your own behaviour, as well as looking at the world around you; I mean, are you a Nihilist or not?! One's self is also very much under the remit here. There are no excuses in Nihilism. Break it all down. Find a sensible way to live, think about what values are driving your behaviour in the world.
Nothing has any inherent meaning other than the meaning you give to it. So give it a meaning according to your values - that is to say "the behaviours and traits that are valuable to you", as opposed to "your value set" - and just detach yourself from any value structures that don't ring true, or that alienate you. Don't ignore them, or turn them into antagonists in your personal drama - they can still contain useful perspectives and ideas. And you know what? Don't be stubborn about your ideas. You have the right to change your mind about ANYTHING, every two minutes.
Also, if you take this "philosophical path", and believe it, I think that practically you have to never become complacent with educating yourself. Arm yourself with science and language. Have a think about art and music and expression and humanities, and how fucking pointless and meaningless and stupid so much of it seems, but think about their impact and their use. Is it pointless? No. Wouldn't even bother trying to argue that one forward. Realising this and feeling comfortable with it could allow you to re-enter passions in an entirely different way, and even.... gulp.... experience love, enjoyment, socialising, beauty etc. in their proper place, while still maintaining a personal philosophy that might appear staunchly negative and cold to anyone who couldn't relate.
Or think about how you could simply reconceptualise an idea like "Love" semantically, and have an entirely new useful and solid perspective on the idea in one simple sleight of brain, which would enable you to enact it in a genuine and fully participatory manner. Make it make sense to you. Think it through and find a position on it. It isn't just a cliche, it isn't imaginary just because you can't find a suitable position on it or move past your (unnecessary) conceptualisation of it. What we call love feels good for a reason, yes, procreation. We get it. All animals are motivated towards it by biological reward. Humans developed language, and with it came self description. It's not crude. It's crude in every other sentient being, we do it for recreation because we recognise that reward as a privilege of our own bodies, and don't just rut blindly, impelled to procreate. Do we.
There's probably a "name" or a value judgement to describe your outlook and lifestyle, if the detachment from that tribal mentality leaves you feeling cold, and you want some stability in your personal and philosophical identify as an overarching Nihilist. It's a bit like being a Marxist, like - ok, now what?
I agree - what you absorb from your parents, their environment, the wider environment and your peers is such a large part of the basis of your identity, it's surely really not a big leap to see how a person could end up feeling very isolated and pointless if they don't apply this sort of thinking in a constructive way.
I can sympathise with you, but there are always ways, because as a truly objective party you can always step back one more perspective, and say that your worst thought has no more meaning than the most mundane, nor the most profound. You would just say "I react to my experiences, according to my expectations, which I have the freedom to fully set and adjust in the face of new evidence, which I am continually receiving. I am not static."
Don't get bogged down, don't sulk, just use it well. You're beer-bonging the malt whiskey of Nihilism and going straight to the drunkeness of the despair lurking between the lines.
I'd suggest that the ideas of Zen would be useful to you. It is very much compatible, with a very basic and narrow central tenet that uses your strength - your ability to objectively discern. Zen is discerning what you have the power to change.
What you don't have the power to change, is "what is". If you have the power to change it, it is not "what is". You develop the skill of becoming sanguine in the face of what is, and you motivate yourself in the face of "what isn't and can be changed". With one golden rule - you can't change other people.