I learnt at school that you use perfect form + ever with "This is the first time", such as "This is the first time I have ever eaten sushi."
But I recently encountered "She was the first girlfriend I ever had."
Are they both fine? Is it because it is past tense? How about present tense?
Are they both OK?
Your question is really about adverb placement. You should do some research about this, and you will find there is often room for variation.
Your second example...
She was the first girlfriend I had ever had.
... isn't wrong, it's just unnecessarily long. People don't think too hard about things like this when speaking extemporaneously. If that's what you're trying to capture in your prose then it's fine.
Your first present tense example is incorrect. This is because 'ever' means eternally into the past or into the future. You can't talk about the present that way. So, "she is the first girlfriend I ever have" makes no sense.
You could say:
She is the only girlfriend I will ever have.
Although a bit presumptuous, it is grammatically correct because you are looking into the future.
But your last example is fine because it is looking into the past:
She is the first girlfriend I have ever had.
This means she is your first until now.
