The underlying purpose of "foresaking all others" is the belief that one has (someone) "committed" to meeting their needs physically and emotionally.
There is no need to "foresake" all others in order to be (platonic friends or roommates) with the same last name.
Unless there is a some medical issue which cannot be addressed I would view sexual incompatibility as a "deal breaker". Natually everyone is entitled to have their own (deal breakers).
Leaving is more honorable than cheating.