Now, this does not mean that restricting marriages by number or the number of spouses by number is unconstitutional. It would come down to what the state claims is the state interest being furthered by a restriction on how many numbers of spouses a person can have legally recognized by the state. There can be stated a legitimate state interest here in several areas. That bar is actually really low. It is when they try to limit marriage based on sex/gender that we find that the state cannot even meet that low bar because tradition is not a valid state interest (or it would have worked when it came to restricting marriage based on race). They cannot prove that marriage is restricted on sex/gender based on procreative ability because that is not a consideration taken into account for opposite sex couples. They cannot prove that children are worse off with same sex couples than with opposite sex couples, and that has zero to do with marriage to begin with (procreation nor childrearing is a requirement of marriage, nor can it be shown to be the purpose of marriage being recognized by the government).
There would be nothing illegal in itself for straight males to marry one another for monetary benefits alone when same sex couples are allowed to marry. There is no test for love or question about what sexuality people are when they seek a marriage license from the state. It would be wrong and likely deemed unconstitutional for the government to even investigate such a thing unless the couple is asking for some significant benefit directly from the government that they must approve, such as military benefits for spouses or immigration benefits for a spouse. The government cannot prove love, which is why love nor attraction is a legal requirement of marriage.