Part of women's liberation is being not financially dependent on men, especially through marriage.

If you look at the cases of military marriages in the US as example, the situation we imagine is that some 18 year old women right out of high school marries a boot for the financial benefits. This basically a direct exchange of sex for money. Some communist writers have made very direct comparisons between monogamous marriage and sex work. A generally accepted opinion on hexbear is that sex workers are good but forcing women into sex work is bad.

I think really you're asking the wrong question. The question should not be "Should people who violate PLA military marriages be punished?". The question should be "Why are there women who are financially dependent on military marriages?" The answer is that they shouldn't be and if women weren't financially dependent on the marriage, they can just leave the marriage instead of cheating. The answer is that a communist society would move away from enforced monogamy.