Kevin Costner and Christine Baumgartner reunited under one roof — but don’t get it twisted, they kept their distance. The reason? Their son’s graduation, not a reconciliation.

Peep the pics — the exes hit pause on the drama for their 18-year-old son Cayden’s big high school graduation in Santa Barbara … but they made damn sure to keep their distance.

Kevin and Christine each gave Cayden his moment — just from opposite ends of the school grounds. The teen kept things Switzerland, snapping pics with both proud parents.

Yeah, the tension’s still there — no mistaking that … especially with Christine still cashing those Costner checks. Remember, Kev handed over a $1 mil lump sum per their prenup and is still dropping $63K a month for the kids.