It's like any neurodivergent situation where certain things just take work. There's specialized apps that allow alters (personalities) to communicate and co-ordinate things like scheduling. From folks I have talked to there's a lot of masking involved where folks with DID will collaborate across different alters to try to appear to be contiguous. A lot of the time from the outside they just seem kind of forgetful in a similar way that non-DID people can be. The source of DID is often severe trauma where the different personalities are created via partitions of memory so that no singular expression of self remembers everything all at once. This allows the whole to function as each peice has functionally a job to do. It's at it's core a coping mechanism taken to an extreme but it still functions as a coping mechanism.
Often times you really don't know someone you've been around for years has it because they are scared to tell you. DID has a fair bit of stigma behind the condition.
This presupposes that marriage is a strictly religious tradition - which is false. Marriage as a concept exists across many cultures sometimes as a religious tradition and sometimes as a civil one or as a swearing of personal oaths.
It is also not strictly a thing that all religions abhor same sex unions or do not have traditional same sex marriage as a thing. There are a number of Indigenous religions across the world which have gay marriage as a feature, new religions can factor them in as valid or existing religious sects can change. Bans on gay marriage force the state to adopt the traditional Christian stance on marriage at the exclusion of other religions and cultural traditions... While also denying a number of functions at a civil level such as spousal benefits, rights regarding legal decisions, visitation rights in hospitals and so on.