There is an almost strange level of trust in there, because even though he definitely had been uncomfortable, pushed farther emotionally than he was really ready for, Phillip did trust that it wasn't Gustavain's intention. Despite where they both have stood, what they both are, he knew that the Warrior of Light would almost never intentionally hurt him, and if he did, it would be purely physical and because he felt like he had no other choice.

Luckily, they are now well past that, and if nothing else Gustavain is right that they both want this. Each of those thrusts is followed by a pleasured noise, the roughness not at all a problem in this case and claiming nature making it all the more desirable. It's still a little difficult, to let go of it all and just feel, but each movement seems to take him further and further away from his thoughts and closer to just this moment.