:sl:
I don't think that you can even think of marrying that girl anymore because her marriage has been already arranged and according to a Hadeeth, it is forbidden for a Muslim to propose marriage to a girl who has been already asked in marriage by another Muslim brother. So the best option for you is to move on.
When you give up something for the sake of Allah, Allah substitutes it with something better.
I'd give you this Dua, use it. It worked wonders for the person who used it and let me tell you who that person was.
Abu Salama (RadhiAllahu Anhu) was on his deathbed when he taught his wife, Umm Salamah (RadhiAllahu Anha) the following dua:
Inna Lillahi wa Inna Ilayhi Raaji'oon, Allahumma jurnee fee museebatee wa akhliflee khairam minhaa
Umm Salamah (RadhiAllahu Anha) recited this dua after the demise of Abu Salamah. Thanks to Allah who accepted this Dua of hers that she later got married to Prophet Muhammad (SallAllahu Alayhi Wasallam). Allah substituted her husband with the best human ever known. And before getting married to Rasoolullah (SallAllahu Alayhi Wasallam), she received proposals from Abu Bakr Siddiq and Umar Farooq (RadhiAllahu Anhuma) as well but she refused. Here's her story:
May Allah guide you and protect you in this time of trial and bless you with a more beautiful and more pious wife.
Don't make vows as well because Rasoolullah (SallAllahu Alayhi Wasallam) didn't really like people taking oaths and asked them to avoid it as much as they could. Have a look at the following page which gives the Ahadeeth of Books of Vows and Oaths from Sahih Bukhari
http://www.islamicity.com/mosque/sun...i/078.sbt.html
:w: