It would 100% depend on the nature of the relationship.
If it was a bit of a fling, fun, nothing serious - I might cope....
If I had feelings for the girl - I doubt I'd make it through her first shift at work without losing it.....
I think I'd be OK (and the I think is huge) dating an ex-WG (say, as an ex-client).... but it would still be doing my head in to some degree....