Yes. What you are doing is completely and totally okay if you are both comfortable with it. In the U.S., there are no state laws against dating or marrying your third cousin.

I would imagine that you are asking this question because there are many regulations against cousins marrying. The majority of states prohibit first cousins from marrying and a few also prohibit second cousins. These laws vary--if you are interested, check out the marriage statutes by state.

On the whole, these laws exist because of the increased risk of birth defects from children born of close blood relatives. Studies vary in terms of determining how risky these unions are. The basic principle is that when two blood relatives have a child, they both share similar recessive genes which are more likely to appear and to contain detrimental traits.

These are the rules in the U.S., but there are cultures in the world that actually place value on marriages between close blood relatives. According to Robin Bennett, a medical genetics researcher, there are cultures in the Middle East, Asia and Africa in which 20-60% of the marriages are between close blood relatives.

But back to you and this guy... It is great that you both like each other. And perhaps there is some slim chance you would have to deal with teasing or remarks from people but I think that would be the worst of it.