If your boyfriend becomes offended when you suggest talking to your friends about him, it's probably because he doesn't want the word to spread that he's taken. He's keeping the connection a secret for whatever reason, and the more people who know about you two, the more vulnerable that secret is.
If your boyfriend is always hiding his phone from you, he might be trying to hide some inappropriate pictures or videos of you. Be sure to ask permission before posting anything of yours on social media, as well as any other content he wouldn't want everyone to see.
If he tends to pull away from you when you try to talk about what's going on in his life, then he might not want to hear anything bad about himself. Just like you don't want to hear anything negative about yourself, so too should your boyfriend not have to deal with this type of behavior from you.
The number one rule of relationships is to be honest with each other. If your boyfriend isn't ready to take this step yet, perhaps it's time to find someone else who is willing to go there with you.
If a person gives you more information than you need, it might be to make it less evident that he's concealing anything from you. For example, if he tells you that he goes to school in California but you never meet him there, this could be because he doesn't want you to know how close he lives to Washington D.C.
Keeping a secret relationship can be difficult at times, especially when you both have things to hide or mask. He doesn't want you to know about his past relationships or problems with alcohol. You don't want everyone to know about your financial situation or lack thereof. The longer both of you keep something like this hidden, the more difficult it will be when it comes time to tell each other everything.
If you suspect that your boyfriend is hiding something from you, ask him directly what it is. If he refuses to tell you, then maybe he isn't ready to tell you yet. Give him time and space; it may not happen right away but eventually he will open up to you.
Remember that you are friends first and only partners second, so keep that in mind whenever he keeps something from you.
He conceals your relationship. There is no cause to hide in a good relationship. When you keep something hidden, it typically signifies you are terrified of someone finding out, you are embarrassed or ashamed of it, or you are both. This might make you feel unworthy of being his public girlfriend. He could be keeping your relationship a secret for any number of reasons, some which are understandable (like not wanting to hurt you) and others which are not (such as feeling like he has to protect her).
Extended Definition: A form of etymology in which the origin of a word is explored beyond its basic meaning to examine all its possible sources and meanings. For example, "secret" can have origins in languages such as Arabic that have many words for "hidden." The extended definition would explore these other meanings of secret.
So, what does it mean when your boyfriend keeps your relationship a secret? It means he's trying to hide something from you or possibly himself. He may be afraid you won't accept him if you know about his past or he may just want to preserve his privacy. Whatever the case may be, this behavior should alert you that there is something wrong in the relationship. It may be best if you stay away from each other until he is ready to tell you about his past.