Change is inevitable. He has changed into this person.. a person who is more tired after work and a person who isn't interested in interacting and socializing much..if not at all. All bodies are not the same. He may require more sleep and may tire quickly now. Although you may feel as he is living an unfulfilled life now,, he may feel differently.
Some people find great peace, fufillment and are very happy with being homebodies and having minimal interaction with the outside world.
It's unfortunate that perhaps your expectations when entering or somewhere along the line in this relationship perhaps excluded this current situation as a future possibility.
It's unfortunate that you seem to have relied mostly on him and family friends for your social activities, and social needs...instead of cultivating and exploring new hobbies, interests, developing and nurturing new friendships on your own.
It's sad and unfortunate that perhaps you two may be incompatible now, and that you two don't spend much time together as you would like. It's unfortunate that you feel alone and lonely in your relationship.
It's unfortunate that he perhaps may be having a difficult time coming to terms with how things are now too..
If you remain, it's best to develop hobbies, interests, and new friendships..on your own.. perhaps therapy may be beneficial for you to help you adjust and perhaps come to some sort of acceptance to this transition in life..
Perhaps if you choose...it may be unfortunately best to part ways. You two are just have differences in life that don't align as before. Therapy unfortunately can't fix the loneliness that you feel in your relationship, nor will it "fix" him. If you leave, perhaps you could find someone that you're better suited for in this phase of your life. An active, full of life social person.
I'm sorry that you two are going through this.