In The Warriors of Kyoshi, Sokka was given a kiss from Suki. Â In book 2, when traveling to Ba Sing Se, he was really happy to see her, and was excited when he heard she was coming to Ba Sing Se, (although it was Azula, Ty Lee, and Mai). Â In book 3, he demanded to know where Azula had taken Suki, wasting their solar eclipse time, and then rescued her from the Boiling Rock prison.
However, most of their love showed after book 1, since we didn't see or hear of Suki until The Serpent's Pass in book 2. Â And in book 1, Sokka really seemed to love Princess Yue, since he was was very sad that she was already engaged, loved spending time with her, including protecting her during the siege of the northern water tribe, was sad when she said they couldn't spend time together even as friends, and was so depressed that she "died" and became the moon spirit. Â His love for Yue was also shown in The Serpent's Pass, when Suki remarked that the full moon was beautiful, and Sokka became depressed.
Sokka really loved Yue, and also got a kiss from her just like Suki, in her spirit form before disappearing in book 1. Also, Suki wasn't around for quite a while, letting Sokka have romantic feelings for another girl, Yue.
If Princess Yue hadn't "died", been engaged, etc, and her father would have let Sokka marry her, who do you think Sokka would have chosen--Yue or Suki?
Who do you think Sokka truly loved the most?