What texts describe a desired behavior when a personal conflict could affect a professional decision?
While I am not aware of any formal universal code (there's not much formal universal anything in academia), the generally accepted scientific ethics is that a person with a known conflict of interest should not be involved in reviewing another's scientific work or proposal.

Most scientific organizations where this might apply have explicit policies to this end.  For example:


Grant reviewers for the US National Science Foundation are not allowed to be submitters to that same call for proposals, and must recuse themselves (i.e., leave the room) when there is discussion of any recent collaborator, co-author, or person from their institution.
Journals typically ask authors to name people with known conflicts of interest who should not be asked to review.  Reviewers are also asked to declare conflicts of interest and recuse themselves, and editors are (occasionally) responsive to well-founded complaints of prejudice.
Conferences similarly ask reviewers to exclude themselves from any papers they have a conflict for, and prevent reviewers from seeing information about any paper they have a conflict of interest for.
Double-blind reviewing of any of these is intended to mitigate the effects of personal conflict, though it is often possible to identify an author anyway due to their topic and approach.


There is no responsibility to collaborate with a person you have a conflict with though, nor to ensure civil interactions at conferences, etc.

All of these systems are quite flawed, of course, and there are a lot of ways that personal conflict does leak into decisions, especially since in many cases it is difficult to distinguish from legitimate intellectual disagreement.