Not being a scholar, as far as I have understood "to like" or even "to love" someone of opposite gender is no way a sin, the fault of Zuleikha (The wife of Aziz of Egypt) was not her loving Joseph --peace be upon him-- but that she expected a forbidden relationship with him and she had a husband at the time. However, if someone likes someone else of opposite gender should either try to marry that person, though if possible at all, or try to get aside from that person's way not to fall in any sin.
Not only touching is forbidden but also seeing each other's body (even if hair or arm or neck or ears of the girl, or body of the guy) and even smelling the girl's perfume is Haram. If any of them may see the other to enjoy what he/she sees this would also be Haram, even if it is face or hand. Moreover they should try to speak seriously not to get even close to the zone of the sins. If they are at a point to decide whether to marry or not they can both see each other (even if necessary each other's body except some exceptions) and speak as much as is required for making a reasonable decision. However, if they have decided to marry and want to spend time with each other before wedding and etc. they should note they are still strangers and not Mahram, and there is no difference between them and any other two strangers of the opposite gender.
The best way however is to do marry in a temporary fashion (النکاح المتعه), this is what I did when I was to marry my wife. Temporary marriage was permitted by the holy prophet --peace be upon him and his household-- and there is a verse in Quran that allows it, but Umar then after forbade it (Sunnis think differently of this history though), but Shi'ite still approves it as a verse of Quran cannot be rejected by Fatawa (Fatwas) of other people.