They had been together off and on for years- ever since they were in college together and Tony was sick of even pretending to study for their exams.
The first time he'd kissed Rhodey, he'd been half-drunk on no sleep and was mildly terrified he'd get punched in the face. Instead Rhodey hadn't fought him- he'd been active participant, pulling Tony closer as he deepened the kiss. It had turned into a regular thing, where whenever the two of them were stressed or overworked, they would make out until they forgot why they were so stressed.
Much to his surprise, they never had sex while they were both at MIT. Tony slept around and he knew Rhodey did too and it wasn't a lack of desire that prevented it from happening between the two of them. During his more introspective moments, Tony thought it might be because he was too terrified of chasing away the first person that he was sure cared for (loved) him for who he was and not what he could do. And Rhodey never pushed him for it. Sure, he pushed him for everything else (eating and sleeping at regular intervals were really overrated) up to and including kissing, but he never did for sex.
They didn't have sex until years later.
Throughout their careers, Rhodey and Tony had been attached at the hip. They'd had to hide more- Rhodey loved his job and Tony wouldn't risk Don't Ask Don't Tell ripping all of that away from him. So he'd forced himself to be content with touching more then strictly necessary, stolen kisses when only Tony's AI could see them.
It had worked until Rhodey was fighting against something or someone- Tony didn't remember, and frankly, didn't care for the details- and it had absolutely destroyed the War Machine armor. Rhodey was in the hospital and Tony couldn't fix him, couldn't help, so he'd done the one thing he could do, which was fix the armor. The entire time Rhodey was there, he worked. He had to build it again from scratch, make it strong, more resilient, able of protecting Rhodey from every single thing that came after him.
He slept in the workshop, unwilling to admit that he couldn't face the world outside with the knowledge that he might not see Rhodey again.
So, once he was healing, once he was able to make his way down and was sick to death of Tony's self-imposed exile, Rhodey forced himself in. They argued, of course, about Rhodey risking his life and Tony thinking it was his job to keep him safe and he'd failed at that, damnit. They'd argued until Rhodey had given up trying to get him to shut up by his normal means of talking over him and he'd kissed him. (Tony always stopped when Rhodey kissed him, it was hard to resist giving in and was so easy to focus solely on the feel of Rhodey against him.)
By the time Tony could even think about it, they were half naked and Rhodey was muttering angrily to him, that Tony needed to take better care of himself and that running himself ragged wasn't going to fix anything- hell, it wouldn't even keep Rhodey safe and fucking hell, when had he gotten so skinny?
They hadn't had sex that night, Rhodey insisted he needed to sleep (in a real bed Tony, not on the couch). The next morning, though, when Tony had woken up more refreshed then he'd felt in years (since the last time they shared a bed in college), neither of them could think of why all their excuses had mattered before.
After- when both of them were sated and wrapped around each other- they didn't speak. They didn't really need to, really, they had always understood each other intrinsically. Tony was done chasing other people like they could ever give him what Rhodey did and Rhodey knew, in the end, with DADT repealed, he didn't have to hide anymore.
Kissing was still a good way to distract Tony from when his mind was racing too quickly.