Perhaps love was like this. Many things and feelings would subtly change with time. When he calmed his heart to explore, he realized that there were already some things in his heart that were taking root and sprouting.
When he married her, he did not actually think of liking her or caring about her. He just felt that he did not really care about these things anymore. Moreover, they were allies, so he could not bear to see her being rejected and feeling disappointed, also...
Hence, he spoke up in the end.
At this stage, he had actually not expected it. However, he did not feel that he could reject such a feeling. At least, during this period of time, he had at least felt a little happy and filled with anticipation.