Tommy Cabot Was Here by Cat Sebastian

Massachusetts, 1959:

Some people might accuse mathematician Everett Sloane of being stuffy, but really he just prefers things a certain way: predictable, quiet, and far away from Tommy Cabot—his former best friend, chaos incarnate, and the man who broke his heart.

The youngest son of a prominent political family, Tommy threw away his future by coming out to his powerful brothers. When he runs into Everett, who fifteen years ago walked away from Tommy without an explanation or a backward glance, his old friend’s chilliness is just another reminder of what a thoroughgoing mess Tommy has made of his life.

When Everett realizes that his polite formality is hurting Tommy, he needs to decide whether he can unbend enough to let Tommy get close but without letting himself get hurt the way he was all those years ago.