The most important thing in any relationship, especially long distance, is communication. Look man, you have to help yourself first, if he's going to keep acting like a first grader and saying, "NO. You did something I don't like! Go away!" You guys are NOT going to get married. Do you even want to marry a first grader anyway?
Just talk it out with him, maybe do a spell to get him talking but that's /it/. The rest you have to do YOURSELF. WithOUT magick. You have to communicate your feelings and remind him you guys are engaged. If you two ain't talking, why are you engaged? Huh?
This could be sprung up from guilt of what he's done of course it could also just be he thinks he's a saint and doesn't tell no white lies. Or maybe the "little thing" to you is a "big thing" to him. Another thing is, he can be VERY stressed right now. This is just utter blasphemy, you're engaged! You guys are adults! You should be above the, "She said something I don't like! So I won't talk to her anymore till she says sorry!" tactics.
Dayum. There's no need for magick for this when you've got ears and a mouth, remember to also LISTEN to him. Don't just talk, give each other a turn to say what's all on their mind. So please, be a bit more like your age and write him a letter and mail it to him or attempt to work it out on webcam or something. Make it intimate, remind him of why you're engaged and if he thinks it's such a big deal, he simply isn't the one you should marry.