It really comes down to the two people involved. Watching any of the so-call daytime court shows on television you will see many cases where exes are in court. One person claims the money given was a "loan" and the other person claims it was a "gift".
The vast majority of people we date or enter into relationships with seldom lead to marriage. It's also been said that 50% of marriages end in divorce.
Keeping this in mind you might want to draw up a promisory note if it's a "loan" and have the boyfriend/girlfriend sign it. Be careful about "volunteering" money to someone who did NOT ask for it. (After the breakup they will be sure to remind you of that). I can't tell you how many times someone calims a gift (became a loan)AFTER they dumped someone. Suddenly the "giver" feels used after learning they were being cheated on or whatever. Last but not least don't give away money that you (need). Even if it is a loan make sure in your mind that you will be fine financially if the person doesn't keep their word. "I'll pay you back when I get my income tax refund....etc" Refuse to become a human ATM.
Bottom line any money given in a relationship is (an investment) in that relationship. If it doesn't work out then you write it off as an bad investment. From what I have observed it seems women have a harder time adopting that philosophy than men. Odds are if you do get married you're not going to be paid back either! :-)