Suppose I am trying to optimize purely for altruistic impact , should I stay single or pursue a romantic relationship? Is there any relevant social science on the casual effects of each on productivity?
Intuitively, it seems like being single would be more useful since you would then have more time to dedicate to work. On the flip side, being in a relationship might help cut costs enabling more donating and could increase happiness to have an indirect effect on productivity?
Alex Foster's answer covers most of what I wanted to say, but I'll also note that thinking in this way...
...is unlikely to be conducive to a successful romantic relationship, unless this thinking is secondary to thoughts like "I really like this person, they make me happy, and I also want them to be happy".
(There's a word for a relationship you form to cut costs, and the word is "roommate". There's a word for a relationship you form to increase happiness, and the word is "friend". As a bonus, it's easier to have multiple roommates or friends than it is to have multiple romantic partners.)