Crisis on Earth X, the CW's two night Arrow-verse crossover event which brought characters from The Arrow, Supergirl, The Flash and Legends Of Tomorrow, saw a passionate kiss between Russell Tovey's The Ray, and Wentworth Miller's Citizen Cold.
If you're looking for the backstory on these two, you can read up on the intricate storyline here. If you're just looking to watch the kiss, you can do so below, starting at 3:17.
Watch:
https://youtu.be/2pZ1u58ynuo