US Immigration from Spain

I am from Spain and I had some doubts regarding visa eligibility.
Basically, I obtained a J1 visa to be an Au Pair in 2016 and during my two years as an Au Pair, I fell in love with an American. When my time was up I returned to Spain and we got a K1 to get married as we were going to spend some time in the US before settling down in Europe due to some personal circumstances of his. It got approved this past March and I traveled to the US at the end of May; however, during the summer we came to the realization that marriage was not a good idea for us and decided to break up. I came back to Spain before my 90 days were up. With the J1 I also followed every single rule and guideline. Between the J1 and the K1 I returned to the US as a tourist under an ESTA permit and I returned under an ESTA permit as well last October (that time they interviewed me at customs regarding the K1 and why I had not gotten married).

I am now gathering all the necessary paperwork to apply for a masters program in the US, however I must take the GRE exam and I am struggling with it, so I am not sure I will actually make it into the master's program this year. Because of that, I started considering the idea of applying to be an Au Pair again for a year while I study for the GRE and increase my chances of being admitted. (Reasons to be an Au Pair instead of waiting it out in Spain are the opportunity of using English every single day, the opportunity of meeting with the college advisor in person, fulfilling a dream of living in a specific part of the country and that it is a program that covers my living expenses while allows me to save some money to use for the master's -- being an Au Pair in Europe, for example has way worse conditions and any other kind of job won't give me as much freedom to save up)

It does worry me, though, that the succession of visas might be an issue.

Any opinions or experiences with this?

Thank you so much to whoever helps out. It might be a silly question and not present a problem, but I rather have some insight into all of it beforehand.

We are in process for K-1 now and our case is at NVC and hoping I can be in US by May - June and immediately get SS then married and apply for AOS as fat as we can.

I didnt find much info when looking online, but they had mentioned to my fiance at the interview for reserves that they can speed up the process when he joins (if he passes that will be in May) but i am not sure if they realised it was K-1 and not a spousal visa or what process they meant exactly.

Does anyone know if it is possible to speed up AOS if he is in reserves? I care more about AP as my best friend is getting married and she asked me to be the maid of honour but with current AOS EAD and AP processing times it doesn't look like I could make it

Thanks!

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I just got the approval travel authorization documents but i need the advance parole document to travel outside usa. Do you know how long does it take to get the advance parole card in my mail after the approval? I have tickets for going to spain next week

They said that even if I take the driving test they wouldn't be able to submit anything, so that I have to wait until my green card comes through. Is this correct? Shouldn't they honor the validity of the visa?

Thank you!