Why would a good online friend delete all your messages back and forth and no longer contact you?

[Lunicolil7]

I have Twitter as a social media network and love it. I've been using it for about 3 years. About 2 months ago, someone started messaging me on YouTube and we became great online friends, until he suddenly started to forget to reply, and soon he stopped replying once and for all. So I asked him why on Twitter, and apparently, he deleted his YouTube because he wanted to take it to the next level with a girl but she just wanted to be friends, and YouTube reminded him of her too much. He said we could message on Twitter, which we did-we direct messaged each other. But it wasn't a lot, and like he did on YouTube, he started lacking in replies, and then last week stopped replying. I gave him time but when I logged onto Twitter today and checked my messages, our conversation wasn't on the direct message list anymore, which meant he must have deleted the messages, right? I messaged him today, and the message went through, so he didn't block me or un-follow me. But I'm a little worried. Plus, another Twitter friend I've direct messaged with ever since I started Twitter, hasn't messaged me for a week now, but I think it's because he's studying for end of year exams. At least that's what he told me when I asked him about 2 weeks ago because it was taking him a long time to reply. I'm not worried about him too much but my other friend who deleted the conversation (I'm guessing) and is no longer replying. Ideas why he would do this, how I can 'get him back', and if he really deleted the conversation or if it's a Twitter thing?
Sorry for the length of this question.
Input is greatly appreciated.
Thanks and have a great day, Blessings!
@wishnuwelltoo I totally understand if you're not here this weekend.
he messaged back 'sorry i was sick and tired'. Just to make a point, he's not my boyfriend or anything. In fact, he's the one who started messaging me. I think maybe I should just end it. Messaging on social media sites only messes things up, I assume since I've seen other questions on this site about topics like these. Thanks to everyone!