The custom of marrying daughters in order of their birth is not Islamic, your parents have to give you in marriage first before you fall into haram relation again. Their acceptance of the proposal is not a marriage contract and hence, he is still a stranger to you and you must not have any type of communications with him.

I am a girl i was in a haram relationship we broke up,repented. Now he proposed to me for marriage and wants to talk to my parents. I have told my parents about the guy they agreed to get me married to him but they wont allow me to marry before my elder sister.Now the guy and me are we in an Islamic engagement? If yes can we wait for 1 year before we can fulfill the marriage contract?

Marriage Contract, Pre-Marital Relations | September 7, 2015 3:00 am
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Sheikh, please, what is the position in Al-Islam of children born out of wedlock? (1) As to the sins of the parents. (2) Will Allaah accepts the worship of the children if they truly practice Islam and die in it. (3) If the parents truly repented are their sins and that of the children forgivable by Allaah? What should they both do.
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I’m 22 years old, and I live in USA for most of my life. I fall in love with a Muslim guy, and he loves me back but we are afraid of getting in haram. we are not able to get married now he is still not stable for marriage. and my family has refused many men have purpose to me, and my family wants me to get my education done first. Can we have sexual relationship before marriage?