Michael Lohan -- Everyone Needs Addiction Help

Michael Lohan tried getting his ex-fiancee arrested, claiming -- just like he did with daughter Lindsay Lohan -- his primary concern is getting the people he loves off drugs.

TMZ has obtained

on December 21. Lohan says, "My ex-fiance, Erin Muller, threatened me with a knife during an argument several months ago and I wish to pursue charges."

Lohan then goes on to say ... "I did not report this at the time because I wanted her to get help for her addictions."

So what changed for Michael? Well, for starters, Muller had him arrested on December 14 for allegedly violating a restraining order against her.

So much for addiction help.

UPDATE: Erin's lawyer is disputing Michael's allegations, telling TMZ she "did not threaten Michael Lohan with a knife."

The attorney also tells us that Michael "is starting to realize that Erin really doesn't want anything to do with him. He needs to take a hint and go away."