[Regex] How to match this: every single-character word followed by a dot

Hi! Due to a error in my action script every space " " around a dot is gone "."
Tags Like Mr. Big are now Mr.Big, this is not what i want.
But on the other side tags like H.E.A.T. are now how i want.

Tl;dr i wanna place a space " " after any dot "." that is followed by a word with more than a character.

Possible Matchs( What i want):
/erv. s--> erv. s
/a.b --> a.b
/aF.k--> aF. k

What i don't want:
/dg. b.-->dg.b.
/g.h.t.-->g.h. t.
/k.o.ph-->k.o.ph

Plz Help me on this one! Still new to mp3tag and regex
Thank you so much for the time you wasted with my topic
Filipe Cruz

It is not quite clear to me what you want exactly.
If you want to find those that have at least 2 letters, followed by a dot then you can use a filter like this:
%artist% MATCHES "[A-z][A-z]."

If you want to replace such a pattern, you can use a format string like
Format string: ([A-z][A-z]).
Replace string: $1._
(where the underscore _ represents a space character)

Action: Format value
Field: ARTIST
Formatstring: $regexp(%ARTIST%,'.([^.\s]{2,})','. $1')
From:
Princ.e & The New Power Generation
To:
Princ.e & The. New. Power. Generation

DD.20160526.1912.CEST