We got Daniel Starr leaving a Starbucks in Ventura Wednesday, and our photog asked him point-blank if he ever hooked up with the actor's estranged wife when he was living at the Costner's beachfront guest house in Carpenteria.

It's not a random question ... the Sun reports Kevin confronted Daniel about his relationship with Christine, claiming the 2 were spending lots of time together on the property while Kevin was off filming.

Daniel was kinda coy when we asked him if there really was a confrontation -- but he was clear about any alleged cheating ... telling us they never hooked up, and were just friendly with each other.

No beef here, according to Daniel ... he says he has no problem with Kevin, even though he moved out a few months before his 12-month lease was set to end.

Daniel says he only had a landlord-tenant relationship with Kevin ... and he's hoping the estranged couple can resolve their divorce amicably for the sake of their children.

While it seems Daniel had a front-row seat to the end of Kevin and Christine's marriage, he doesn't want to speculate about what led to the split ... and it sounds like he just wants to make a clean break.

As we reported ... Kevin claims Christine is refusing to leave the home, and she now wants $248k a month in child support.