Cant see why he would unfriend you if he is truly a friend and understands that you are looking out for him and you will support him 100% either way. A good friend wouldn't just stay silent. Every single one of my friends that have gotten married I told them good luck but I wouldn't do it if I were in their shoes and jokingly (but seriously) told them to rethink the decision, maybe live together for a while and have a kid etc......marriage is supposed to be forever right? so whats the rush. Never got unfriended or anything childish like that. Some are still married, Some are divorced, most are very unhappy in their married life and 2 or 3 seem to be doing ok.
One of my buddies had a raging controlling bitch of a girlfriend and of course I let him know she was bad news and he must be crazy for wanting to marry her....they got married, then got divorced after a very shitty 2 years. The girl had him locked up a few times for "spousal abuse" that never happened. We are still very good friends. He is still rebuilding his life.
nobody has ever been able to give me any clear positives to getting married out here in the west, not one. Its a fucked up deal for the man and only a foolish man would go into it. A ridiculous and worthless gamble IMO
Don't get me wrong, I believe that true friends should respect/appreciate each other's opinions, but the thing is that not every person can handle that. In case he can't, it can result in an inner conflict with unfriending as a result.
For example, one of my friends is a HSP and is pretty safe in his way of communicating (no homo & no Getbigger, LOL!). He's the kind of person that I won't bother too much with my sincere advices or thoughts, esp regarding personal choices. Only a very tactical way might work, but I'm much too direct for being a diplomat, esp when I see potential problems.