Though not an issue within Tyson’s main universe, he doesn’t get upset by the idea of Moran and Moriarty being together. He encourages it.
There are several reasons for this. Tyson is poly and openly admits to loving both Sebastian and Jim, he isn’t someone who gets jealous, and he is overjoyed by the idea of having someone else around to encourage them to actually take care of themselves.
As stubborn as Tyson can be, he can only dig in his heels so much when it comes to Moran and Moriarty. He wants them to be the best that they can be, the happiest and healthiest. If being together made Moran and Moriarty happy, Tyson would do anything in his power to keep them together.
Yes, Tyson would be overjoyed to be a part of that relationship, but equally, Tyson would be content on the sidelines and know that the people he loves are happy together.