My idea is similar. Another question I have is where does it cross from loyal to sharing. Is it sharing if you flirt with someone, maybe share a kiss, are you allowed to be attracted to other people ? Or is it loyal until you get to third base.
A good question with a variety of answers, depending on scenarios and discussions between those concerned.
For mine, loyalty stays at the point where there is no physical or emotional contact with others, slight as that might be. Everything else is either cheating or sharing, depending again on discussion of consent, or it is cheating without discussion. So, "first base", not "third base". Everything about "first base" progressing to "third base" or beyond, needs discussion, preferably at the "idea" stage, not after.
A man or woman who gets touched, groped, kissed etc by any other, is a cheat, if they don't immediately discuss it with their significant other, and make suitable adjustments immediately, put simply.
The question about attraction is a bit of a furphy. It is human nature for both sexes to find many other people attractive, constantly, married or not. Its what you do about those thoughts that define your relationship.