Why would this be sloppy seconds? If that's the case - isn't everyone who takes back a cheating spouse getting sloppy seconds?
Yes. If they take back a spouse that is still "cheating" aka sleeping with someone else.
In order to take back a WAS they have to WANT to try again. Have to agree to a FULL NO-CONTACT LETTER and FULL PRIVACY DISCLOSURE. If not they are wasting your time.
Ofcourse that's my opinion. Once again. Life is way too short to be with someone that is not "sure" if they want to be with you. Living with someone else as a backup plan or vice versa is not someone that I would take seriously.