<human>: My current girlfriend I met at college and my ex-girlfriend (with who I cheated on my current girlfriend with) I met at school and therefore have known for quite some time.

I recently went on a trip with my friends from school (my ex-girlfriend is in my wider group of friends so I often see her during such gatherings). I brought home some of my ex-girlfriend's and another friend's stuff because they couldn't manage it. I had been talking to my ex-girlfriend a bit over the trip and I am ashamed to admit that we'd been flirting a bit.

When my ex-girlfriend came over to collect her things she stayed and watched TV for a bit, we started flirting and we ended up having sex. The entire ordeal lasted no longer than a couple of minutes (impressive, I know), and once it had finished the reality of what I had done sank in. I became angry and inconsolable, my ex-girlfriend left and I've been a wreck since.

I 100% am going to tell my girlfriend, but I wanted to do it in a fitting setting. The next time I meet up with her face-to-face will be a week and a half after sleeping with my ex. Now I could force a meeting earlier than that, but considering she is about to move into a new flat and has a lot on her plate I was going to wait (only 5 days after she moves, no longer) until she had her things sorted then go over and talk to her.

I'm sure telling her will greatly upset her and I think it will make her move a lot harder than it needs to be and she might not even manage to do it at all (she's currently temporarily living at home).

Is it ok to wait so long to tell her so that she's more stable living-wise or should I somehow meet up with her to tell her earlier?

Any advice on how best to tell her would also be appreciated. I would give anything to manage to reconcile things after me being an absolute shit.

Can you succinctly summarize the text in 1-3 sentences?
<bot>: Cheated on girlfriend, going to wait 1.5 weeks to tell her but don't know whether I should try and tell her sooner although this could seriously disrupt her move.