Oh wtf they weren't even exs, I thought they were at least dating in the past then broke up. And like she secretly still like him or something so now there is a chance for it to go better for them. But the harem is so wtf and out of place.
The irony is this whole plot would had worked so much better if they didn't show her at the start. And just show him having miserable life and then suddenly going back in time. And she just happen to be the first person he meets after he returns in time.