Best situation he could have ever wished.
1) Tell Mami "We obviously still like each other, but let me break up with Chizuru first"
2) Talk to Chizuru, "break up" with her, Mizuhara goes back home, Ichinose goes back to her friends.
3) Enjoy your former-ex-now-new-new-gf, no need to rent a gf anymore. Happyly ever after.
But since this is ch.10 and there are already 85, I guess that is not what happens next.