It does seem to me that it's about time that you meet his family, and I can empathize with your frustration and feelings about this issue. It's a long time to be in a relationship and not feel like you're a part of certain parts of his life. I understand if he's feeling insecure or nervous, or if he's had some bad experiences in the past, or whatever it is that's causing this "block", but if you've been together for four years, and you've been understanding and supportive up until this point, then I think he needs to bite the bullet and at least introduce you to his family. It doesn't need to be a big, long, involved meeting, but I think it is appropriate for you to be a bit more firm with him and explain to him why you feel like this is important to you. Perhaps if you can outline your feelings about it and explain how you (for example) want to feel like you're an important part of his life, and that meeting his family would help you feel more comfortable with that. But as far as not saying the word "love", I think there might be some bigger issues going on here than simply being socially awkward. When you combine this with the fact that he hasn't introduced you to his family, then I have to think that he's maybe dealing with some sort of an anxiety
disorder - social anxiety disorder, perhaps, although it's not really possible to say without meeting him in person, of course. Especially since you say he has problems conversing, is secretive, etc. There might even be the possibility of some other mental health concerns, but he'd need to see someone in person to obtain a proper diagnosis (or, even if there is no true diagnostic problem, to determine what is causing these blocks.) And based on what you've said, it does sound to me like he needs a bit of help in overcoming some of these blocks. I'm not sure how you would feel about this, but I think you might want to have a discussion with him about the way you're feeling. You have a right to discuss your feelings with him, and it sounds like you've been very patient and understanding so far. If he's not receptive or he resists discussing these concerns with you, then you might want to broach the idea of couples counseling with him. I think it could help in terms of improving your communication, and it might be a good place to discuss some of your concerns about meeting his family and his not using the word love, for example. Discussing things with a neutral, third party can help you both get a different perspective on what's going on as well as to obtain advice about how to deal with it. Sometimes, people need a bit of extra help, and there's nothing wrong with reaching out to a professional who might be able to help you both get to the root of some of your concerns. If you're interested, you can find a counselor on this website:
I hope that helps. Please let me know if you'd like to discuss this further.