Suddenly wanting to be alone?

You're never wrong for feeling a certain way. These are your feelings and it's ok to have them.

Two possibilities spring to mind when reading your question.

1. You might be suffering depression. This is more likely if you were previously sociable and have recently lost interest in socializing or fun activities you once enjoyed. Are you experiencing any other symptoms of depression? Other symptoms include feeling teary, snappy, or hopeless/worthless - changes in sleep and appetite. If you think you might be depressed, please seek professional advice.

2. You are simply a classic introvert. There may also be some level of social anxiety going on, in which case you may find it beneficial to speak to your GP. In my opinion, this is the more likely explanation as opposed to depression, as you mention hobbies and spending time with family and pets. Many introverts struggle in social situations and feel the need to 'recharge' after socializing. However don't be embarrassed to talk to friends, family and your boyfriend about this. There is no shame in being introverted and there's nothing wrong with craving alone time!

Nah. Alone time is vital, it's normal. I personally think it's abnormal not to give time to yourself, and give all your time to others. Devote more time to yourself and enhance yourself.