Am a Christian and from a very strict and religious Christian family, I love this guy and he began to teach me things about Islam and I fell in love with Islam. We both would want to get married but my family and his are not in support of it. I want to revert to Islam, but don't want it to be because I love him. I also don't want to hurt my family mostly my mom. We've done things that are wrong in Islam and decided to stop. He loves another Muslim sister and it scares me a lot I feel am loosing him already. He said he would like to perform Istikhara so as to do the will of Allah. Now my question is can I also perform Istikhara despite I not being reverted to Islam yet. If yes how should I go about it.
Strictly speaking istikharah is a prayer or consultation-prayer that has been introduced for Muslims in first place.
A short clarification: its pre requirements are taharah -ritual purity- which means one should be Muslim (first), perform (at least) wudu' -ablution- or whatever is necessary to be in a pure state.
Then one should pray a two raka'a sunnah or nafl (different terminology but meaning the same with a slight deviation depending on the scholarly interpretation) before performing/reciting a known du'a -suplication-.
From a more lenient perspective I don't see any harm in if you prayed to God -in the manner you know or learnt- with all your might and conscience in the best manner and ask Him for consultation -you may use the formulation of the du'a or something similar-, you may perform the Muslim wudu' prior to this as it might be a first experience in this matter, and maybe helpful.
Finally be aware that becoming a Muslim for the sake of Allah and the love for him and this religion is a much better reason than anything else.
You may find these posts helpful:
For further information checking posts with the tag:istikharah might be a helpful start.