Proof of affair

If my soon to be ex is claiming I had an affair, including sexual intercourse, what proof does she need for this claim to be upheld.

She will have to prove that an affair occurred by a preponderance of the evidence standard, which means it is more likely than not that an affair occurred. In North Carolina the standard is that an allegation of adultery must be proved by making a showing that there was an inclination (desire and affection between the accused) and opportunity for sexual conduct to occur (normally a showing of time spent together overnight or in a hotel.)