You saw her, first in a bathing suit and then apparently nude, talking to him about her decision to leave the X-Force and about mutants "evolving." He tells her she's "too good" for the team. After, she says that if she's "too good for X-Force", she must be "too good" for him. He then suggestively says, "But you need a taste of poison now and then. Just to keep things balanced."
They aren't shown kissing and unlike what some people have claimed is shown in-panel, she isn't straddling him. She's in front of him, leaning over, with her arms around his shoulders. Now, I'm not saying this scene isn't suggestive because it certainly is, particularly Logan's closing comment. However, there aren't any artistic indicators that they had sex afterward, i.e., no kissing, no groping, no straddling.
Furthermore, outside of this scene, they have shared one, maybe two non-passionate kisses. I just don't see this sexual relationship others do. And, before anyone claims I feel this way because I want Jean to be a "goody-two-shoes" or "Care Bear"--HA!--that's hardly the case. I like an edgy, risque Jean.