Jameis Winston -- Baptized with GF ... In Spiritual NFL Retreat (VIDEO)

Jameis Winston and his girlfriend Breion took the plunge ... sorta ... at a spiritual retreat in Colorado this week, surrounded by a BUNCH of NFL stars.

No, we're not talkin' marriage ... but they did get baptized together at a Pro Athletes Outreach event in Colorado Springs -- an annual event that brings together hundreds of NFLers every year.

The event is geared toward couples -- who pray together, attend workshops together and listen to different religious and motivational speakers.

Among the stars this year ... Antonio Cromartie and Brian Hartline ... and Kurt Warner ran a seminar.