Alright we need to sort some things out here brah.
Problem 1: She is a cheater.
Problem 2: She claims to have been suicidal
Problem 3: She is a liar
Now the third one is redundant considering it coincides with the first. And while I know you said it wasn't sexual, emotional cheating is a real thing so this floozy is a cheater. The suicide thing is something I've never come in touch with, but my friend dealt with two crazy girls who said similar things. Considering its been four years since that and they're still alive, there is reason to be dubious of your cheating girlfriends confession/defense mechanism.
You sit in a place of uncertainty. You're unsure who this person is. It's time we figure out if this tramp is all bark and no bite. Some people will argue vehemently against what I'm about to to tell you, but disregard their opinions. This is about you and the TRUTH.
Here we go.
Rule 1: COOKIE CRUMB TRAILS
Leave loaded guns on various items of furniture and hang nooses(the plural is intentional) from the ceiling around your place.
RULE 2: BE CREATIVE!
Mix the liquor cabinet with the medicine cabinet, a fresh pack of razors on the bathtub edge.
RULE 3: MAKE IT CASUAL
You want to make it seem inconspicuous too. Should she ask about your new "lifestyle", just wing it. If she's really a kook, she'll really be thinking about how she can get her hands on the loaded luger she found between the sofa cushions.
Watch her closely so that you can prevent her from actually doing harm to herself, but you must hold the presence of a ghost. She can't know your around, that'll break the genuineness of it. This is all about the TRUTH. Should she actually do something you will now know that problem 2 is a real problem and problem 3 is no longer as big of a problem.
Once things have been sorted out you've got to leave her. She went around pushing it with other dudes and then laid that psycho jargon on you. This is a running forum. GTFOT