It is safe to assume that when you left the US in 2010, you were "noticed" at the border and placed on a unlawful presence list. If so, it is also safe to assume that you will need a waiver to enter the United States again under a Fiance visa or an I-130. The waivers are challenging to obtain, although as of late there are major reforms on waivers for certain foreign nationals already in the US. I suggest you contact a competent immigration attorney to guide you through the process and possibly look into your case in more depth.
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from 11-18 you were OK and not accumulating "unlawful presence" in the US when you overstayed your 90 visa waiver entry but you were out of status attending school not on a F-1 student visa and valid I-120. From 18-20 you did begin to accumulate "unlawful presence" in the US for more than one (1) year and upon your departure from the US you triggered a 10 year bar/prohibition to returning to the US unless you get/obtain a waiver from the USCIS. SO, the waiver for non immigrants (K-1) or K-3 fiancee visas are INA 212(d)(3) non-immigrant visa waiver is obtained from USCBP in Virginia, from the ARO office but takes up to 1 year. They are not easy but also not impossible to obtain. Once approved in hand with your new K-1 or K-3 fiancee visa you can then come to the US. Or if you get married and then your US citizen boyfriend files an immigrant visa for you for consular processing at your cuntries US Embassy, then you will need to file an I-601 (INA 212(a)(9)(B) waiver for inadmissibility due to having been living in the US unlawfully for more then 1 year and then leavning the US based on extreme hardship to your US citizen husband who would suffer if you are not allowed to return to the US. Again, its not easy but not impossible but probably harder to obtain then the INA 212(d)(3) waiver, since you do have to show that your Qualifing Family Member, i.e. US citizen husband would suffer extreme hardship if you are not allowed to immigrate to the US and join him here. All the hardship is on him not you. On the non-immigrant visa waiver its all on you and no need to show extreme hardship or any hardship really just a reasonable need of why you want to come to the US and why you would not repeat your previous unlawful presence of 9 years if allowed back into the US. You would have to file another I-601 waiver later at the time you are in the US and apply for your green card through your future husband even if you do get the non-immigrant waiver but it would be easier to argue extreme hardship once you have been living with him together in the US for sometime as husband and wife. The non-immigrant waiver is or can be valid for multiple entries and valid from 1 month to 1 year. The immigrant I-601 waiver once granted is permanent and covers any previous violations for ever unless you committ additional violations once in the US prior to becoming a US citizen if you so desire. Good luck.
Based on the facts you describe above, it is most likely that you will need a waiver to enter back into the United States. Waivers tend to be complex and this matter is best handled by hiring an immigration attorney to assist you.
It is very likely you will be required to obtain a waiver. The waiver requires a showing of extreme hardship to the qualifying US citizen or lawful permanent resident relative. You should obtain legal counsel for this process.