There are two circumstances when a man is free to spread his seed, and step outside of his relationship.
1. An LDR. A highly interested woman will follow you to the ends of the earth, or wouldnt dare leave you to your own vices while she follows her dreams. This is assuming a certain amount of reasonable behavior in the mans part ofcourse.
2. When a woman refuses sex. This means she does not find you desirable enough to fvck at that point in time. If you push all of the right buttons, she should almost always be willing to have sex. Periods, exhaustion, and any other reason are mere excuses to avoid your p3nis. A "no" to me is the Monopoly equivalent of "get out jail free" card.
The best way for an LDR is to not do it. For every 1 that succeeds, many more fail. And for every success, think about what they likely sacrificed for that LDR. Maybe they missed on someone who was better for them, or maybe they gave up career opportunities. It's best to part ways peacefully, and possibly reconnect in the future.