She's Brilliant

Maybe if he's feeling guilty enough. Or, if this was a murder mystery/thriller, it would be because the woman was loaded and her boyfriend and the person he was cheating on her with decided that they wanted her cash without the extra baggage of the woman around. So he gets a tattoo of her in the hopes that it will alleviate suspicion from him when he and his mistress kill the woman and try to make it look like a suicide. Of course, that still wouldn't explain how he'd get the woman's money since he's just the boyfriend. Maybe if they were living together long enough? I'm not sure how that works exactly.

The story is true, i wad the tatto.

Well I know in Canada, a certain amount of years spent living together is "common law marriage" which, as I understand it, functions almost identically to a real marriage in terms of taxes and such, as well as inheritance.

That's not true, yes it it is called a "common law marriage" which can have tax benefits, but in the case of death it doesn't hold up (unless there's a written will). Inheritance would go their descendance or other blood relatives.