Paris Hilton -- I've Found My Soul Mate! (PHOTO)

Paris Hilton has marriage on the brain -- her sister Nicky is getting hitched Friday -- and Paris might not be too far behind ... because she's already calling her new BF her "soulmate."

Paris and her super rich new guy, Thomas Gross, have only been together for about two months ... but it's clearly getting serious. The couple was all dolled up for a night out in London -- where Nicky's getting married.

No pressure Tommy boy -- but we suspect someone's gonna be gripping your hand tight during the wedding.