Was it all about looking good?

Mormon missionaries stay in an area for a short time. They transfer to different areas almost every 3-6 weeks, so him leaving has nothing to do with regrets, but just moving on. Try talking with the new Elders at church and make friendships with other members of your ward. If your testimony hinges on how one person (said Elder) acts or doesn't act, then it will quickly fade away. Read the scriptures, keep asking questions, and you will find your own testimony.