i too wonder if he's depressed or worrying about something to distraction.
can you ask him re depressed or worrying bout somethin? it sounds so much like severe depression. how does he act otherwise? that may help you decide if it's depression or not. is he on any new meds like high blood pressure rx? many have a side affect of severe depression...i mean severe. it happened to me, that's why i ask.
what you did re the ring was awesome and the scrapbook you made by hand was so incredibly sweet. i am so sorry things seem to be going south without your understanding why. you love him a lot so i'd pick your moment and sit down with him. tell him how his lack of interest makes you feel. i'd suggest your using the "i feel" words so he doesn't perceive it as criticism.
i hope this makes sense. i too don't feel he's got a gf. hugs