Just to follow up on what everyone else is saying... I mean, it's not really possible to judge how "intimate" it is just from the words alone.
It's obviously more familiar/friendly than just a plain old おやすみなさい! would be, especially if he used that same emote with a red heart and exclamation point that you have in your original post.
That said, to assume that he meant it "intimately" (i.e. in a romantic sense) would be a bit of a leap, as the phrase doesn't carry that inherent nuance.
Honestly, it's really not at all different from if someone said "Good night. Sweet dreams

" with an emote in English.
It's something that yes, you
could say to someone you had romantic feelings for, but in other contexts could also just be a casual thing to say to a friend.
If you're trying to gauge the intimacy of your relationship with a Japanese man you met online, I'd judge it by the type of interactions you normally have with him, the things you talk about etc., etc., rather than trying to read too much one way or another into this one particular phrase.