My take on this when I read it was far too much far too soon followed by did you establish his reason for being on the dating app/his current circumstances.
From your story I can see you met a guy, got on well with him, invested an incredible portion of yourself and your time in him even before date two. After date two you noticed he became quieter etc. It sounded to me as if you were considering yourself more involved with him at this stage, wanting him to contact you even when he might be busy with other things etc.
In reality, you'd only really spent a few hours together which is far more valuable than all the texting etc.
Date three came along and all was wonderful. He was giving the right signs, planning a future etc even though you'd only known each other for five minutes. I mean, it sounds lovely and all but again, the reality is that it's a bit much too soon and it's all got a bit carried away.
He's woken up the next day and, for whatever reason, just not felt on the same page as you. So he's knocked it on the head and rather than tell you to his face that he's had second thoughts or that he's just not that into you any more, he's pulled away and disappeared on you because sometimes that's just how people deal with things.
Frankly, it's been three dates. I've worked a shift longer than you've probably spent together! He doesn't owe you anything. You may think he does because you've chosen to invest all your time, effort and energy into this one man but it's dating. That's all.
Here's the best bit though. You can sit and ponder over a hundred reasons why he's ignoring you. You may even be right on some of them. It could even be absolutely nothing to do with you either. It could be him. That's why I asked if you'd established his personal circumstances and what he was looking for on the site. Many people join these sites for all sorts of reasons and unfortunately many of them shouldn't join at all. Ultimately, I think you could either sit and cry over him and keep texting him, which he will continue to ignore (hoping you'll get the hint) or you can dust yourself off and get back out there in the dating world and find someone who is emotionally and physically available to you, and who does want you.
I think next time it might be prudent to adjust your selection process. Sort the wheat from the chaff. Be clear with what you're looking for and then find someone who matches that. If you're looking for someone to have a relationship with and the next guy says he is too then watch his actions. Take it slow. Invest less of yourself at the start and let things unfold at a slower pace. That way the guy will show you who he is over time and if you don't like what you see then cease dating. Multi date too so you don't put all your attention on one guy.
Try the above and then if it goes a bit tits up next time you won't feel so hurt. You're Cancer/Scorp. You're extremely sensitive so chose wisely with who you open up to.