Why not get legally divorced (but not socially)? As long as you don't get married again it looks like that's not fraud by the IRS. Page 23 of http://www.jefftk.com/abrams2012.pdf has:
"Although the IRS attempted to use Boyter in several subsequent cases
that dealt with divorces allegedly entered into to lessen tax
liability, courts have sided with the IRS only in cases where the
couple remarried after the taxincentivized divorce. In cases where the
couple remains divorced, the sham transaction rationale is not
available. For example, in U.S. v. Taylor, the government sought to
satisfy a tax lien against a man by going after his pension plan—90
percent of which was transferred to his ex-wife in their divorce
proceedings—by contending that the man had obtained a sham divorce in
order to shield his assets.115 The court distinguished Boyter, noting
that while the couple remarried in that case, in the present situation
the couple remained divorced.116 Thus, the test that appears to
operate in the tax context is a “divorce-plus” test: we know that a
divorce is fraudulent if it is followed by the “plus” of remarriage."
I don't want to pay less taxes. I have a philosophical objection to unmarried couples paying less than married couples with the same income. Paying less myself doesn't fix that.
As the cultural and social power and significance of the institution of marriage starts to wear off, more people will start abusing it for the benefits. A lot already are -- my friend was telling of a guy who divorced his wife in the papers purely to get tax benefits, even though they're still together as man and wife.
Also conversely, another mate of mine was suggesting in complete seriousness to another friend of his that they should get married to get nice affordable housing benefits; both male (I mention they're both male because I think if the friends were male-female, social stigma would be stronger, but because they are old buddies from high school, this subject was discussed in a "hacking the system" mindset. It is very interesting to see that the institution of marriage is seeing its power drop, I think years ago people would absolutely gasp at someone doing this, now it's like "woah, cool trick, I'm gonna marry my friend and get in on this too!")
"Although the IRS attempted to use Boyter in several subsequent cases that dealt with divorces allegedly entered into to lessen tax liability, courts have sided with the IRS only in cases where the couple remarried after the taxincentivized divorce. In cases where the couple remains divorced, the sham transaction rationale is not available. For example, in U.S. v. Taylor, the government sought to satisfy a tax lien against a man by going after his pension plan—90 percent of which was transferred to his ex-wife in their divorce proceedings—by contending that the man had obtained a sham divorce in order to shield his assets.115 The court distinguished Boyter, noting that while the couple remarried in that case, in the present situation the couple remained divorced.116 Thus, the test that appears to operate in the tax context is a “divorce-plus” test: we know that a divorce is fraudulent if it is followed by the “plus” of remarriage."