Do you have a friend or other person you care for that has polar opposite beliefs as you? This could apply to just about anything; politics, religion, lifestyle, etc.
Yes, multiple friends and my family. For example, my friend circle includes conservative and liberal Christians, Muslims (of varying beliefs as well), Marxists, Marxists-Leninists, and capitalists, among others.
A close friend is an Islamist--a fundamentalist Muslim who believes in Islam as a political manual rather than just a spiritual one. He knows about my beliefs, and we get along quite well.
Do the differing beliefs positively or negatively affect the two of you?
It depends: with family, I accept them as they are, but I definitely can't come out to them as an atheist. So the difference in beliefs affects our relationship negatively because I can't truly be myself with them.
With my friends, the differences generally don't have much effect compared to personality, general attitude, etc. A TERF friend recently said she didn't want to be friends with me anymore because of my pro-trans views, though, and she didn't want to stop talking about the topic. She couldn't stand the disagreement on that.
I believed she could change her mind at some point (as I did in the past) and stayed open to discussion, but I think her views may be too extreme for that as well, unfortunately.
Do you intentionally avoid bringing up things that might cause conflict, or do you enjoy bantering about it back and forth? Do you believe the friendship is sustainable long term?
My closer friendships tend to last for at least a few years, so yes, they've mostly been sustainable in the long term.
As for avoiding certain topics, that depends on the person: as I've said before on RF, my general approach is to be patient with people and not automatically cut them off even when I think some of their beliefs are deeply harmful or immoral. However, some people are more prone to getting upset than others about certain discussions (e.g., the abovementioned TERF friend), so I adjust my approach accordingly.
While I personally adopt the above approach, I also think that some issues are more personal and serious than others, and I don't blame people for not wanting to befriend others who have certain views that go against the former's basic rights or dehumanize them. I can't blame an atheist for not wanting to befriend an Islamist who believes in killing apostates or a black person for not wanting to befriend a white supremacist, for example.
