Is it okay to fall in love or get attach to your first cousin after having sex with him?

In the bible book of genesis i dont remember the verse it says that it was okay to get married to the first cousin but in leviticus i also dont remember what verse but it says that its a sin to have sex with a sister, brother, step brother, step sister, dad, niece, nephew, mom, uncle, aunt but it never mentions anything about a cousin...
Is it okay to fall in love or get attach to your first cousin after having sex with him?
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