This article in The Guardian discusses in detail a paper just published in JAMA Pediatrics, co-authored by Julia Raifman, Ellen Moscoe, S. Bryn Austin, and Margaret McConnell.
The first link above leads to a nice explanation of the results of the paper, and the second leads to an extended abstract that readers who are adept in econometrics (and other statistics-savvy people) will want to read closely.
It seems to me that the marginal benefit of same-sex marriage legalization includes the saving of many lives. The marginal economic cost is negligible, if it is even positive, compared to such a marginal benefit. Individuals wishing to argue that the moral marginal cost outweighs the marginal benefit will find it very hard to convince me of their case.
UPDATE: I changed “suicides” to “suicide attempts” in the title of this post for higher accuracy.