I would take the "or" out of your question. Yes, he definitely is very immature AND that is a serious issue. Failure to mature is one of the worst issues an adult can have. I'm afraid you are in for a roller coaster ride with him.

Start now by setting precedents that will push him in a more mature direction, though you've got a heck of a lot of pushing to do. He has no right to open your mail or inspect your cell phone. Insist on your rights on these matters. You are not an extention of him, but a separate person. Start being very clear about what he has a right to access to and what he doesn't. This business of lovers checking each other's cell phones -which I hear a lot about these days - is a violation of one's rights to what is personal. If you let this intrusion into your space go by, you are giving him permission to disrespect you.

You will never get him to respect you by pleading with him. You've got to stand up to this firmly. He has little respect for others. That BTW is what speeding is all about. Speeding in a car as brazenly as he does it (7 tickets!!) says "I will not accept anyone putting limits on me!" So you'ld be wise to do exactly that . . . set those limits! Say, No trespassing on my phone." He will disregard and test you. Then you have to give a real consequence - like no contact with him, until he apologizes. Soon you will have a child on your hands. Actually, you'll have two children.

That's real nice that he was sweet when you were sick, but it's not okay that he will offer you sweet devotion, IF you give him total control.