I totally understand, being a former junkie myself. Hopefully I can share some tips about how to get into the mind of the Magic addict.

With regard to your relationship, there are a lot of things you can do. Trying to cut him off of it will not end well. I have been there, it's not going to work. It's an addiction, much like gambling - treat it as such.

Instead, start by finding ways to spend time together in the context of the game, or similar games. Try board games. Games like Dominion and Netrunner are low-cost and have huge appeal to Magic players. These games are sold in defined sets, not random packs, and have no price inflation due to popularity (unlike Magic).

A game night with just the two of you, or even with a couple card shop friends might be a good place to start. Hosting Magic drafts at your place is also an option. Get into the social group - it might not be your favorite thing, but distancing yourself isn't going to change anything.

Learning a little about Magic would be a good way to help reverse the alienation - you're going to have to get into the muck if you want to dig him out. If Magic is what he pays attention to, that's how you have to hook him. As him to teach you how to play. Read the FAQ at /r/magictcg. Watch StarCityGames tournament coverage once you get a handle on the game.

You must start with compromise. A hard line will get you nowhere. You are dealing with an addict, so you must rehabilitate him. That begins with showing alternatives to the game, and being a part of the social group. Give him a new thing to do that is like Magic, but involves you. Reconnect, and move forward from there. If that fails, then getting him professional help is probably your best recourse.

P.S. From a financial perspective, there is a correct way and and incorrect way to approach Magic. Here's how to make the game not break the bank, which may ease some tension in the short term:

1. DO NOT BUY BOOSTERS TO BUILD DECKS. NOT EVER. Buying singles is ALWAYS cheaper, 100% of the time. Shop at tcgplayer.com for the best prices.
   
2. Build one deck and stick to it. Standard rotates on a 12-15 month basis. If you spend $300 on a deck and play it for a year, that's not a bad rate. The game rewards experience, and skillfully piloting your deck. Buying the flavor of the week is a great way to get broke and still perform poorly in competition.
3. Buy multi-format staples when possible. Some cards are only expensive during the current Standard rotation, and will lose all of their value once the current Standard ends. Cards that are heavily played in the "eternal" formats, Modern, Legacy and Vintage, will hold their value over time. The fetchlands in current Standard are a good example of staples that are worth buying (Flooded Strand, Polluted Delta, etc). Research these cards, and find as much overlap as possible.
   
4. Pay attention to the metagame and trends. What decks are doing well? Prices of those cards will increase. What decks do well against the decks who are winning? Prices of those cards will soon be increasing. SCG coverage results are a good indicator, along with mtgtop8.com.
   
5. Watch prices and speculation at /r/mtgfinance or mtgstocks.com. Pay attention to what cards are legal in Standard, and when they rotate out.