I'd guess you're probably happy because you get the benefits of a relationship without the day-to-day headaches. I say this without knowing any of your details, of course. But it's the same reason why affairs are such an attraction for everyone.
You get the physical love, the dating, the attention... But you don't have to put up with him when he's sick, or deal with his financial issues, or do his laundry when you've been working all day... What's not to like? You get to keep your house the way you like, and don't have to negotiate or compromise.
The drawback of course is that you'll never fully have him. Eventually, you'll grow old alone. You won't have anyone to take care of you if you're sick, or having a really crappy week. His family will likely take priority when you want to do something and he's got family obligation. You won't have the benefits financially of a joint relationship, being able to fund a retirement together. I'd say these are the reasons your family says you're wasting your life. You may be happy now, but what does the future hold? Are you moving forward to any kind of future relationship, or just treading water?