Derek Jeter's Ex-GF: I'm Not Jealous of Hannah Davis ... Seriously.

At least one of Derek Jeter's many MANY famous ex-girlfriends is thrilled for him now that he's engaged to Hannah Davis ... telling TMZ Sports, "He's living his dream."

We spoke with model Vida Guerra -- who dated Jeter way before Jessica Biel and Jessica Alba -- who tells us she's genuinely happy #2 found his #1.

"He said once he retired he wanted to get married .... so he's living his dream. Congratulations to him."

Question is ... is Vida jealous that Hannah got the rock and not her???

We asked. She answered. Check out the clip.

Oh, and also check out Vida's hot modeling pics to see what Derek's missing out on. Damn.