To ask if this would bother you?

[lemondrizzlecakes]

Say you became really good friends with your next door neighbour, and you separate from your DH. You move out, ex gets a new girlfriend and she moves in. The new girlfriend becomes friends with the neighbour, would you be bothered by this?

Now I feel like I can tell this friend certain things, in case it goes back to ex IYSWIM.

I can see where you are coming from but I'd try not to take it personally as it's her next door neighbour it puts her in an awkward situation as it would suck to fall out with them being so close? Agree I would hold back on details you wouldn't want to get back to him, sorry if it's changed your friendship

What gin said. Is she also friends with your DH?

If she was exclusively your friend and the new woman was the OW then I might expect her to not become friends with her but otherwise id just be mindful if what I say to her because of making her feel awkward

YABU. You've moved, your neighbour hasn't. She's got to live there and falling out with neighbours over trivia is never worth it. Get over it.