Actually, Soarin is a minor character, the writers don't choose or develop the minor characters making them important because he's not important. He is one of the ponies who had problems of friendship and loyalty. The only pony who works with her is zephyr, but said no character would not fall in love, since lot of people would be disappointed.
Spitfire is a wonderbolt too and with him is her second-in-command, Rainbow dash helped her heroes to get togerher again, bring back Soarin to the team (replacing him by Dash, and they repent) and Spitfire the same (the episode after she was blamed for a crime that she did not, and Soarin is glad to see spitfire again). They cared for each other and thanks to Dash's help. In the comic it was also the same, Spitfire worries by Soarin, and also the help brought him back, the Dash's help too. Both with her was loyalty, trust and friendship to each other, never interaction etc;
He is not even in a relationship, both of them have a different personality. Quibble pants and even Spitfire had a personality very similar to Rainbow Dash and while Soarin is quite and shy as Fluttershy and respectful. I am shipper but I don't declare them as canon, we're just playing and watch them as one and something that wouldn't work.