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!

[wishnuwelltoo]

I don't know anything about twitter, but I think the person studying for his exams is really studying so let that go for now. I think the other person is probably dating new gf and maybe she doesn't want him talking to a bunch of old girlfriends and that is reasonable. If you were dating a guy, any guy, you wouldn't want him talking to other girls all day and night when he is supposed to be dating you. He might be using this girl as an excuse, we don't have any way of knowing it. One thing though that I have learned about people.....the issue is rarely the real issue. So maybe you think he ditched you for this girl, but maybe it it something you have no way of knowing.....maybe his dog died, maybe his parents are going through a divorce, maybe he has cancer........sometimes life is funny. Don't take it personal when a person mistreats you, I find that it is always some other thing going on that I didn't know about at the time. I am wondering how you found so much time for twitter and yet you didn't have time to get your homework done. Maybe he felt guilty that your homework isn't done. (just kidding) Hope you have a wonderful weekend. I will be working long hours this weekend, so don't assume I am snubbing you if I am not on my computer this weekend.

[jotacar]

People move on. It looks as though you'll have to do that now.

[hersheynrey]

He is growing up and probably doesn't have as much time or he has a gf and is spending alot of time with her or doesn't want to make her jealous. What ever the reason is he is only one guy and there are millions of other people in the world so don't let the actions of one bum you out or stress you. If he has stopped conversing then oh well , its his loss not yours.