Can I marry my American boyfriend with an expired F-1 visa?

F-1 visa gives you permission to remain in the U.S. for "duration of status"; it means that you can stay in the U.S. so long as you remain enrolled full-time in a qualifying course of study. If your visa states that it is good only through the end of May, it means only that, if you leave the U.S. and want to come back for your summer semester, you need to have all the visa paperwork done and approved now so you could go to a U.S. consul in your country and get a new F-1. But, in your case, it is not relevant. You and your fiance can get married any time - now, before or after your F-1 runs out, before or after your graduation, it does not matter. Under the law, if a) you entered the U.S. legally, b) you eventually married a U.S. citizen, c) he filed an immigrant petition and an affidavit of support for you, and d) you are not disqualified from becoming a permanent resident (by having certain criminal convictions, or for other reasons that I am not going to discuss because they don't apply to you - otherwise, you would not have gotten any visa) - then you can adjust status (obtain a green card), even if you overstayed your visa and fell out of status. Having said that, I must advise you, on the experience of numerous clients, not to spend much time out of status. Being illegal is not good for your soul, for your personal dignity and the sense of self-worth. It makes you afraid. And it makes you feel, somehow, a lesser being than the people around you. Being illegal also can get you arrested, jailed by the Immigration, and deported. Some people seem to be charmed in this regard, and never run into a trouble. Others aren't so lucky: trouble finds them, without any warning. To go through the procedure of adjustment of status, you do not need to leave the U.S. (if you have to, you can, but it will make the process longer). This will be one of the most important legal steps you will ever make; and its outcome will change your life forever, one way or another. It is also an expensive process: the filing fees to the government amount to about $1500 (which you won't get back if the petition gets denied). So do yourself a favor: get an attorney.

You can get married at any time but you should NOT leave the country. As soon as you are legally married you can file for adjustment of status to permanent residence on the basis of marriage to a US citizen.

To avoid any potential problems in the future, you should marry your boyfriend as soon as possible and start the process while you are still in valid student status. After you get married, your husband can petition for you and you can apply for adjustment of status concurrently. Your husband's petition is filed on form I-130 and the adjustment of status application is filed on form I-485.

You can apply for your green card without having to leave the US. This is the case even if you overstay your student visa. The green card process takes about 90 days from start to finish (if done correctly). You should not leave the US during this process.

You should be able to stay here and adjust status after marriage.