Disclaimer: I don't own Sirius or Remus. I only borrow them to write cute little stories.
In third year kissing for Sirius is awkward. Teeth click and noses are in the way. He doesn't now where to put his hands and there are fingers messing up his hair. He kisses three girls before deciding that Andromeda was wrong when she told him kissing was more fun than pranks.
In forth year kissing is a little bit less awkward an a little bit more enjoyable. Putting his hands on curvy hips and tilting his head, Sirius thinks he's at least on the right track to figuring out what Andromeda was talking about. Still, there is something missing.
Kissing in fifth year is like finale knowing the answer to a problem you been thinking about for years. He doesn't mind the hand running through his hair and loves the arm around his waist pulling him tight against a strong chest.
There is no kissing in sixth year, only thoughts of what could have happened and how he could have been so stupid.
But the best of all is kissing in seventh year. In seventh year kissing is like coming home after being away far too long. In seventh year kissing is knowing he has finally been forgiven. Because now there is Remus long slender fingers running through his hair, Remus strong arms around him, holding him so tight and never letting go. There is Remus lips on his, teeth biting on his bottom lip only breaking when absolutely necessary.