There is usually a marked difference between "insight" practice (that give realisation about the fundamental nature of experiences) and "concentration" practice (i.e. jhanas). Just practicing jhanas is not all that conducive to mental upset - you purify your behaviour, focus the mind, suppress the hindrances, and experience intense states of wholesome qualities that take over your consciousness for a while. There's nothing negative or dark about that. But Buddhist practice goes beyond jhana practice by using the power of that focused mind and suppressed hindrances to analyse experience through the lens of the Buddhist teachings i.e. right view. The issue comes about if the analysis comes from an incomplete or wrong view, leading to nihilism. It's best to stick to "pure" jhana practice and not meddle with insight practice if possible, if one doesn't have access to reliable teacher than can correct misconceptions in view that lead to negative outcomes.

The other thing is that "pure" jhana practice, when done correctly, kind of sets up the mind with a kind of wholesome "blank slate" from which to do the analysis that leads to insight. Some traditions, especially those that have been imported as "secular mindfulness" to the west, tend to emphasise just doing that analysis of experience without too much jhana practice involved. If you don't already have a very wholesome mental state (i.e. the kind of mental state that comes about from living in a monastery and limiting the actions and speech being undertaken) then there can be a whole lot of mess to sort through and opportunities for unwholesome states of mind to latch on and become the basis for your worldview. It's not a coincidence that a lot of the narrative and commentary about mindfulness and the "dark night of the soul" (i.e. dukkha nanas) comes from those traditions, but isn't mentioned in other traditions that emphasise practice differently.

Note that "insight" meditation without Samadhi/Jhana practice is sometimes called "dry insight", and a lot of "insight" focused teachers still emphasize Smadhi/Jhana as an important part of practice.

Also note that generally, traditional Buddhism tends to see building virtue in everyday life as a necessary prerequisite for meditation. You can be a lay Buddhist by being virtuous but not meditating, but not the other way around. A lot of people in our western culture tend to approach it the other way, with meditation as the defining practice and virtue as a secondary thought. I remember hearing of a meditation teacher who loved to start meditation retreats by saying something like "most of you would probably benefit more from hosting a family of refugees, rather than coming to a silent retreat", which would upset quite a few participants. If you want to ground this in meditation, practices such as "loving kindness" meditation are very helpful, and can help overcome/avoid a dark night.

There are also other more "modern" "traditions" (if you can call something that is at most a few decades old a tradition) that can help deepening insight into emptiness _while_ also increasing a sense of wonder and respect for the world, rather than falling into nihilism. I am in particular thinking in Rob Burbea's "Soulmaking Dhamma". To summarize it, he proposes that, given the insight that there is no reality without a "way of looking" (his way to summarize emptiness), it is not only OK to embrace a way of looking, but we have flexibility in doing so - and switching between such ways of looking in this way helps deepen insight into emptiness, rather than lead to delusion.

This does not make immune to feelings of confusion and grief, but can help work with them. Also note I am by no way a spiritual teacher, and what helped me might not help you.

To add to this, you're more likely to find someone who experientially understands what you're going through (and how to deal with it) in Buddhist circles, esp. those lineages who primarily focus on meditation (Zen, Chan).

Even if you don't necessarily prescribe to a Buddhist world view, being able to talk to someone who not only understands what you're talking about but has also gone through it and knows precisely how to get through it, helps immensely.

OP, I hope that you and your partner landed and got some intuition about the answer to your question(s). If you want someone (meditator) to talk to, my email is in my bio.

Can recommend "Trauma-Sensitive Mindfulness: Practices for Safe and Transformative Healing" by David A. Treleaven on this particular subject, especially for people working in that space.