Nigel is right about the 'teg'. Also, I think, if one used 'good cariad' at all, it would be Cariad Da. Cariad can be either masc. or fem. but unless you were referring to a specific woman, you'd use the masc.

Except that I can't really think of a situation where you'd say, 'cariad da'. Other adjectives are more usual. I guess because 'da' is a bit bland when referring to love.

sian