Asking for his phone number is not desperate.
If you'd feel more comfortable talking to him that way then ask him. You said he's very sweet to you and he's on tinder so I think it's safe to assume he likes you. He's not going to freak out over such a simple detail.
You do seem a tad obsessed, but as long as you're not bombarding him with incessant text messages or getting unjustifiably annoyed when he doesn't reply immediately then I doubt you're going to scare him off.