What Exactly Can A 3-stone Diamond Ring Be Used For?

I wanted to buy my girlfriend a 3-stone diamond ring instead of a promise ring because I havent seen any promise rings that liked. I like the 3-stone diamonds because they use bigger diamonds, and the just look a lot better than promise rings. MY question is… is it okay for me to give her a 3-stone diamond ring even though we arent even engaged yet? OR is it mainly for married couples? Can i use it as a promise of engagement like a promise ring? Because i know the 3-stone stands for “PAST-PRESENT-FUTURE”… Thanks!

• 1/4ct 3-stone Diamond Ring in 14k White Gold, H-I-J, I1-I2
• 14k White or Yellow Gold Princess-Cut 3-Stone Diamond Ring
• 14k White or Yellow Gold Princess-Cut 3-Stone Diamond Ring
• 14k White or Yellow Gold Round 3-Stone Diamond Ring
• 14k White or Yellow Gold 3-Stone Diamond Ring
• 14k White or Yellow Gold 3-Stone Diamond Ring
• 14k White or Yellow Gold 3-Stone Diamond Ring