if go its was good , if go good and missed its mean

Because if you say "가면 좋았을텐데", the two tenses don't match, so some people might understand it like "I wish you could go" or something like "It's too bad that you can't go"

To be more exact, it should be 갔었다면 좋았을텐데 or 갈 수 있었다면 좋았을텐데 to say "I wish someone were there."

The second phrase doesn't really make sense, but I assume you said(or heard) those two phrases as similar meaning.... and it means "I wish (someone) were there." And you put the Korean word for someone in the beginning of the phrase. Like "네가 가면 좋았을텐데" means "I wish you were there."