David Geffen says he’s ready to move on from his marriage and be an unmarried man again … and he’s even prepared to cut some big checks to his estranged husband.

In new legal docs, obtained by TMZ, the billionaire says he’s willing to pay his estranged husband, David Andrew Armstrong (AKA Donovan Michaels), up to $50,000 a month in spousal support.

The catch here … Geffen says the payments should only last for 12 months and be retroactive to their split … adding he should get credit for whatever he’s shelled out already.

Geffen claims he’s already shelled out $200,000 in cash to Armstrong since they separated back in February … and he says he paid almost $200K for the guy to go to rehab.

What’s more, Geffen says he’s allowing Armstrong to live rent-free in a $15,000 a month apartment he owns in Manhattan’s Upper East Side … and he says the guy has $5 million in art, jewelry and watches Geffen bought.

We broke the story … Geffen filed for divorce in May, and there is no prenup.

In the new docs, filed by Disso Queen Laura Wasser, Geffen says he’s made every effort to resolve the spousal support war … but he says mediation didn’t work out and claims Armstrong tried to extort him with a smear campaign in the media.

Geffen also points out he was 80 and retired for more than a decade when he tied the knot with the much younger Armstrong, and he says they didn’t accumulate any community property during the 23-month marriage … in other words, he says, even though he might get some spousal support, Armstrong ain’t entitled to a split of his reported $8.7 BILLION fortune.

In a separate filing, Geffen is asking the court to terminate the marriage and make him single in the eyes of the law … he says the marriage is “undoubtedly irremediably broken down” and he no longer desires to be married to Armstrong.