To some extent "as they affect your life/who you are".
There is something stilted about erasing every trace of exes from your life. But there's also the "wow, I'm relieved I'm not with him/glad to be where I am" that naturally means that ex doesn't surface every time.
So, I can picture this conversation (early on in da
ting):
Me: ...Blah blah blah D&D group blah blah blah Kender cosplay (note, no, I don't, I just like the idea

)
Date: "oh, what got you into cosplay?"
Me: "one of my exes invited me to game and I discovered I really liked it; I've been involved with the cosplay for about 5 years now and really enjoy the costuming aspects...blah blah blah.
What would probably not go well would be:
Me: ...Blah blah blah D&D group blah blah blah Kender cosplay (note, no, I don't, I just like the idea

)
Date: "oh, what got you into cosplay?"
Me: "one of my exes invited me to game and I really liked it. When we started having trouble, it caused all sort of friction in the group. Now we rotate out who goes to the local store--I have dibs on the first and 3rd weekend of each month and every other wed. But I never go on Thursdays and Tuesdays because he and his new GF are likely to be gaming then..."
OR
Me: ...Blah blah blah D&D group blah blah blah Kender cosplay (note, no, I don't, I just like the idea

)
Date: "oh, what got you into cosplay?"
Me: "uhhh, someone I once knew invited me to a D&D game once and blah....
^that isn't all bad, but...it's unnecessarily 'oversensitive' to avoiding exes--that's the one that may be fine but also may blow up later when suddenly "wait, what do you mean this was something you did with your ex?" is 'discovered'--it's trying to hard to keep secrets
I know that's OTT, but, that tends to be the basic--early on. Later on, how much history you share depends on facets of the rel
ationship that are myriad.