During my adult time, certainly before I got married. I've experienced a quite long period of time of being alone. Yes, I'd friends and family. But I did felt lonely every now and then. That's why when my wife mentioned that some friends of her who are still single in late 30s and how they feel about being alone and feeling lonely, it was quite easy for me to identify or empathize how they feel. I'm glad that I'm not them at their ages. However, as I always believe that 'things have more than one side.' i.e. the 'half-glass' argument about things.
Being Alone is more a physical condition. Namely, you are the only person in your premise. Like you are left home alone, you go driving alone, etc. You live on your own. It actually is a sign of independence. You have all the freedom you want in your premise. You can be selfish and expressive without being considerate. You don't need to reach consensus or compromise. 'You eat what you cook!'
Being lonely is psychological. It is a feeling that you have. You can feel lonely on a busy street. It doesn't really depend on the physical environment.
So, being lonely doesn't mean being alone and vice versa. Being alone is demanding, like you need to be able to afford that, like renting/buying your own place to live. Or having your own car. Otherwise, you need to find a place to be alone is not easy for most citydwellers like us. For example, if your are living with other folks, and suddenly you want to be alone in the middle of the night. You can only lock yourself in your bedroom and put on a headphone. Otherwise, I wonder where can you go? Being lonely is a feeling usually only happen when you are not busy. i.e. got nothing to do and your mind can float....and think....and drift.... Or when you want to do something, but you can't find anyone that can accompany you. Busy people are not lonely people.
So, there are a lot of trade-offs for this topic. Some folks want to be alone, but they don't want to feel lonely. So, the work hard to afford living on their own, and work hard to keep contact with friends, wooing lovers, and joining group activities. In other words, they only want to be alone when they want to be, like after party to go home, and don't bother me when I don't want to be bothered. However, as I mentioned, most of folks that my wife mentioned to me are able to do just that. However, they just can't do one thing. It is that 'others' are not always available when they want them to be around. Cos, those others do have their own lives. They may have their friends, family, and other engagements as well. So, it is quite often that those lonely folks have to work hard to plan things ahead for Friday evening and weekends. Also, they do have to adjust their expectations and satisfaction thresholds on being with others. Cos, those that they really want to spend time and those end up they spend time with could be....different. They need to learn to settle for less.
For those folks who live alone, they may not need to develop hobbies that are for loners. Surely, they can read books, listening to music, doing photography of still objects or scenery, watching movies, jogging, swimming, playing racket ball, etc. Activities that they can enjoy or at least do alone. However, for lonely folks, they better try to do the opposites, like going to learn ballroom-dancing, rather than hip hop. Join tennis club, football club, rather than taking pottery-making class. To be more social and meet people, that's the way 'out' from being lonely. If they really wanna go for something long term, even going to dating services or match-making services would be advisable. Just need to be open-minded. Cos, I think that the wall between lonely folks and the rest are built by the former. They built it and they have to tear it down themselves. Being lonely is all in the brain!