It looks like a 168.1220 DeVille Prestige from late 90s or early 2000s, with a caliber 1120 (ETA 2892 based). This is my first time eyeing one of these, but $2500 USD doesn't seem like a fantastic deal. There's one identical (with the same BOR bracelet) in Chrono24 for $1900 and another sold in eBay for ~$1700. In a forum I saw it listed for $800 without bracelet.
What other Omegas does your boyfriend have? Are you looking for a vintage piece or a newer design? If you haven't already decided on this one, I'm sure we can give you some great alternatives for that much money or less.