How does ic affect sexual function?

IC is Unrelated. Male or female sexual function should not be affected whatsoever by ic, since the functional and psychological aspects of each are independent of the other. Voiding before intercourse could alleviate the "urge" to go during sexual activity as in the case of a full bladder. This could help make activity less pressured and more enjoyable. Functional orgasm and ejaculation should not be affected.
Depends on severity. If you have a lot of pain and urgency relatd to the ic, and it is aggravated by intercourse, why would you want to do something that hurts. You tend to avoid behaviors that cause pain. If the ic is not affected by intercourse in terms of pain and urgency, there is no worsening of the ic by intercourse.