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.
The most correct opinion of the scholars is that what should be taken into account about the result of the Istikhaarah prayer is what happens. If the thing upon which the Istikhaarah is performed is facilitated and it takes place, then there is good in it, but if the matter is made difficult and it is not possible to achieve it, then abandoning it is good.
As regards feeling one’s heart opened or closed (for a thing), then this is not evidence to follow it with Istikhaarah either to do that thing or to abandon it. It should be noted that many people perform Istikhaarah while they are possessed by their desires either to do or not to do a specific thing, so how can they consider feeling their heart opened or closed as evidence for them?
In any case, if the result of the Istikhaarah is what we mentioned, that what should be considered is whether or not the matter is facilitated, then there is no need to ask whether fearing committing fornication is a reason for neglecting the Istikhaarah.
Therefore, if that young man is religious and has a good moral conduct, then you should perform Istikhaarah about marrying him, and it is permissible to perform Istikhaarah more than once as clarified in Fatwa 88342. Then, if he asks you to marry him, then you should accept him as a husband. If there is any good in him marrying you, then Allaah will facilitate this marriage, otherwise, Allaah will drive him away from you. So, to Allaah belongs the command [i.e. decree] before and after (i.e. the whole matter is in His Hands). Moreover, this young man should perform Istikhaarah about marrying you as well.
However, we do not know how a person can authoritatively assert that marrying a specific person is or is not beneficial; therefore a person should perform Istikhaarah in such a matter in any case.
Nonetheless, in case this girl and this young man are not facilitated to marry each other, then they are both obliged to cut any relationship and avoid anything that may lead to temptation or Zina (fornication or adultery).
Allaah Knows best.