When someone ruins all the good they have ever done!

I would say that such people are "self-nullifying". "Nullify" is defined by Merriam-Webster as "to cause (something) to lose its value or to have no effect".

I can't think of a general example but in the specific circumstances you gave, of a friend ruining a friendship by acting badly, it is said that they've burned the bridge with you.

Wordreference.com has a good definition:

This is an idiomatic expression that all English speakers understand. To burn bridges means to suffer the ultimate consequences of personal betrayal: termination of relationship.

Obviously this has a rather stronger meaning than the phrase you seek; if you burn the bridge between you then you leave the relationship so damaged that it is impossible to return.

EDIT: You can be sure that this phrase is established by the fact that it is found in the Cambridge Dictionary:

If you are in a situation and you burn your boats/bridges, you destroy all possible ways of going back to that situation.

Reminds me of this epic Chinese proverb that goes, "One moment of patience may ward off great disaster. One moment of impatience may ruin a whole life." But it doesn't get any truer than the way William James wrote it "Act as if what you do makes a difference. It does."

You can describe such a person as a Jekyll and Hyde.

a Jekyll and Hyde

someone whose personality has two different parts, one very nice and the other very unpleasant

Usage notes: This phrase comes from the main character in the book The Strange Case of Dr Jekyll and Mr Hyde by Robert Louis Stevenson.

You can't depend on him to be friendly - he's a Jekyll and Hyde.
_{The Free Dictionary by FARLEX}