All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
First of all, we thank and praise Allaah Who guided you to Islam and we ask Him to make you firm and steadfast on His Religion until the Day you meet Him. This is indeed a blessing for which you should be grateful to Allaah.
Dear sister, you should know that the majority of the scholars are of the view that it is forbidden for a woman to travel without a Mahram, but some scholars made an exception to this for the woman who is travelling for the obligatory Hajj and obligatory ‘Umrah in the presence of a safe company. Also, she is allowed to travel without Mahram in case in necessity, like when migrating from a non-Muslim country to a Muslim country as we clarified in Fatwa 84377. Moreover, some scholars are of the view that it is permissible for a woman to travel (without a Mahram) in any travel that is an obedience to Allaah provided the journey is safe.
Therefore, since the case is as you mentioned in the question that you are in need of this travel, then it is permissible for you to travel to that country if the above condition is met while observing the limits of Sharee'ah, like observing the Hijab, avoiding staying in seclusion [with non-Mahram men] and avoiding forbidden mixing with men, and it should be mentioned here that this fiancé is a non-Mahram to you as long as he does not conduct the marriage contract with you. Therefore, in case you travel to his country, it is forbidden to stay in seclusion with him, and both of you must avoid everything that is forbidden between non-Mahram people until the marriage contract is conducted.
Also, it should be mentioned that there must be a guardian who would conduct your marriage contract with a Muslim man, either it is the Muslim judge or whoever acts on his behalf, and if not, you should appoint a trustworthy Muslim man so that he would conduct your marriage contract [marry you off to that man]. For more benefit, refer to Fatwa 88488.
Allaah Knows best.