The no-longer-new girlfriend wants the divorce to happen. The ex-wife wants the divorce to happen. This sounds like an excellent opportunity for the two of them to team up and fall in love.

(My guess is that if the divorce happens, it will not be just legal expenses, but the ex-wife finally getting money/assets she should have had access to decades ago. But if the current girlfriend and wife team up to get him a quickie for-fault divorce on the basis of obvious adultery I suspect he will be even worse off!)