friends w benefit, arranged marriages, poly...
A few things:
Is polyamory allowed within the confines of his tribal marriage, or would sex with you be considered cheating? If extracurricular activities are not allowed, it's simply not ok for you to be a part of causing chaos in the lives of his wife and (eventually) children. He has a responsibility to other people now.
If it is allowed, then you have to ask yourself if you're willing to live life as an afterthought. You have indicated that you are, so:
How long are you willing to put yourself in this position? You know this situation is going to end in heartbreak, so you just need to figure out how much time you're willing to give it. If you don't need a committed relationship or a family of your own anytime soon, then you could throw several years or so away. But, if you would rather invest those years in what you really want out of your future, it might make sense to make other choices.
Is polyamory allowed within the confines of his tribal marriage, or would sex with you be considered cheating? If extracurricular activities are not allowed, it's simply not ok for you to be a part of causing chaos in the lives of his wife and (eventually) children. He has a responsibility to other people now.
If it is allowed, then you have to ask yourself if you're willing to live life as an afterthought. You have indicated that you are, so:
How long are you willing to put yourself in this position? You know this situation is going to end in heartbreak, so you just need to figure out how much time you're willing to give it. If you don't need a committed relationship or a family of your own anytime soon, then you could throw several years or so away. But, if you would rather invest those years in what you really want out of your future, it might make sense to make other choices.