He's sick of it by this stage, but there's nothing he can do – there's no chance he wants to give this new life up just yet, so he'll just have to deal. The most depressing part is how both of them, the Doctor and Rose, think they're being discreet in front of him when it's patently obvious that the reverse is true.
He'd thought he'd seen the last of it the other day, after the incident with the Pompadour woman. But when he'd gone to find Rose after dinner, she wasn't in her room or in any of the other usual places. He hadn't been able to locate the Doctor, either, although if he's honest, he was somewhat less than thorough with that particular search. The harder he searched the more suspicious of the TARDIS' motives he became. He didn't put it past the ship to be steering him away from wherever Rose was, because he had the oddest feeling that wherever she was, he would also find the Doctor.
He had given up in the end, and gone to bed; searching for somebody who obviously didn't want to be found – or at least not by him – was never any fun and he'd soon become bored, in any case. In the morning he'd woken up earlier than usual. He'd opened his door to find Rose meandering down the corridor with a soppy smile on her face. She'd been dressed in what looked very much like one of the Doctor's shirts and precious little else, and it didn't take a rocket scientist to figure out where she'd spent her night, or who with – or what they'd been doing. He'd backed into his room and stayed there until the time he normally went to the kitchen to fetch himself some breakfast, unable suddenly to stomach the idea of the two of them being all over each other as would no doubt be the case if he'd gone there any sooner.
He's happy for Rose, he really is. He's even happy for the Doctor, believe it or not; he can see how much happier the man has been now there's somebody in his life that loves him for him. Something tells him that the Doctor hasn't had an awful lot of love like that in his life. It isn't as if he didn't know what he was getting into when he challenged the Doctor to let him on board the TARDIS so that he could take part in an adventure too. He's known that Rose and the Doctor are an item since that night in a pile of Sycoraxic ash last Christmas (last Christmas for him, at least; God knew how long the Doctor and Rose had been travelling since then). He knew he wouldn't be able to break them up and return to the status quo ante he and Rose had enjoyed. Not that he'd been trying to, but that wasn't the point.
But oh is he sick of it, all the same. Knowing something to be true in principle and seeing it for himself have become two painfully different things. Face facts, he thinks to himself, it won't get better for you than this.
He can't stand it any longer, and it's not as if Rose needs him any more. The Doctor's started giving him "keep off" signals, so he can't interfere there even if he wanted to. He feels strangely empty, and thinks that there have to be other ways to find a better life. Maybe it's time he found one of them.