The fact is that Q is thin enough that Bond can easily lift him up and pin him to the wall with ease. There really isn't anything that Q can do to stop him; he's hardly got any muscle, just skin and bones. He's taken the necessary self-defence classes (he barely passed them) and he does know how to fire and hold a gun without injuring himself.
None of that changes the fact that, if he really wanted to, Bond could easily overpower him. The only thing stopping him is the simple fact that Q is someone who Bond wants.
Bond is relentless. He comes, he pins Q to the wall, and takes what he wants. Q finds that he likes it; he's turned on by that dominance, that force, the way that Bond can easily pick him up and shove him against the nearest solid surface and fuck him senseless within minutes.
He likes all of it. From the way Bond holds him up, to the way his fingers dig into his hips so hard that they leave behind bruises, those he treasures. Everything about Bond is hard-edged and dangerous and Q loves that; he's attracted to that danger and that promise that there – underneath all those hard-edges and ice blue eyes and cold words – is something more.
For now it's all rough sex and a sensual torment that he cannot get enough of and he's fine with all of that. But there's a small part of himself that he keeps tightly locked up that hopes for something more that he will never ask for.
Until then, there's the sex and it's enough. Each of the marks, each of the bites, those he keeps to himself; covered up by clothes but the ache is still there and he remembers. He waits until the next time, the next fuck, and tells himself that it will be enough.