People do change over time and sometimes feelings as well.
I believe things between you guys are going downhill, and the only way to actually fix it is by talking to him about how he feels about you and you guys’ relationship.
I know you’re missing the “old him” but regardless if its the old or new him, it’s still him, his feelings just probably changed. Only he knows what made it change and if you’d like to know, you can personally ask him. Don’t rely on having people messengers because stories and words will get twisted.