You have already failed your mission by not leading with your conviction! You should have screened your partner for before considering them!
Serious answer: Idk, whenever it feels natural. Truthfully, it isn't something that has to be on your sleeve in "real life" even though it influences you. They don't necessarily have to know. I wouldn't consider it that serious.
I think you should mention it to a partner at some point. This place inherently ties into my opinions on world events and politics, and also gender, sexuality, and feminism, so I think I would need to share this part of my life if a relationship was really cooking. But I agree it's not the only thing that features in those, and isn't the most important thing in my life.
I see it as mostly harmless to disclose when it comes down to it. It's just an internet forum that their partner would have to look into more thoroughly to decide whether it is good or bad. I don't consider it anywhere near as bad or toxic as some right wing spaces, so it isn't like you are showing your partner you love going to /pol/.
not as toxic no, but still very extreme and likely bewildering to the average person if they stumbled on here. I wouldn't show someone this until I knew they felt safe with me, so that they could properly contextualize this and not misunderstand the discussions of violence on here.
A lot of people kinda shut down when they see non-standard violence. Like, once you endorse shooting someone who isn't committing a crime, many get scared about what you want to do and only see the violence, whether what you're endorsing is ending the inherent violence of homelessness by ending landlords, or shooting minorities