It is not "bad" to want to date anyone. If you want to have sexual relations with a cousin, that is more that going on a date, and some people are uncomfortable with the thought. However, even so-called blood-related cousins can marry -- second cousins everywhere, and first cousins in about half the jurisdictions of the US and I many other places as well.
Whatever you want.
You can date anyone you want, whether third cousin or first cousin. Going beyond simply dating may raise issues with a first cousin, but not with a third cousin.
Certainly, you can date anyone you want, including your cousin. But your cousin's step-brother is not related to you, so questions of relationship do not arise. It's about equivalent to dating your cousin, so it's up to you if that's against your morals. As for genetics, having a child with him won't produce abnomalities if they don't share a biological parent with your cousin, but as for ethics, it's up to you. If the parents of your cousins step-brother are related to you no. But if they're not go for it!
It is not proper to date your first cousin. He is part of your family and a close relative-- too close to date.
No, you are related like it or not. But, once you are grown, you don't have to associate with your cousin if you don't want to.
Your first cousin's wife is not related to you because you share no common ancestor. She is your uncle's daughter-in-law, so she is your cousin-in-law, if you want to stretch a point.
Yes, if you want to.
Absent any other twists... your sister's boyfriend is also your cousin, for example, so that your sister's boyfriend's cousin is your brother or something... it is completely fine to date your sister's boyfriend's cousin if you want to.
yes miley is my cousin and her grandma is my ccousin and grandma
But I don't want to date anybody, I'm married.
You can, just not legally. Also you have problems if you want to date your cousin. It is also legal to marry your third cousin.
You can marry whomever you want. Morals are a different story.