Is it okay to marry a second cousin?

The law is usually not prohibited (maybe the Russian Federation is an exception, I don't know).

From the point of view of genetics - normal. Siblings (brothers and sisters) share 1/2 genes. Cousins ​​(descendants from different siblings) - 1/8. Second cousins ​​(descendants from different cousins) - 1/32. When a second cousin is married, the probability of a particular harmful recessive mutation in the offspring, which was in one of the sibling's parents, is 4 times less (you need to get a mutant variant from both parents). That is, 1/128.

For comparison: when cousins ​​are married - 1/32 (and this is allowed in most countries). When a brother and sister are married - 1/8, parents and children - 1/8, uncle and niece (nephew and aunt) -1/16 (these options are usually prohibited as incest).

But if from generation to generation to marry relatives (albeit not very close ones), then the genetic diversity will fall and recessive mutations will certainly appear.

In general, you can marry anyone, even your own brother. The main thing is, if you want to have common children, check with a doctor for common recessive genetic diseases and if they do not exist, then there are no problems, and if there are, then the children in your family will be exclusively adopted.