I only have one friend that plays ARMA and we are mostly online at different times but when we do get together we voice chat through Steam and do short co-op missions together and that brings a whole extra level of fun. You don't need loads of mates or to join a clan to get into the MP aspects. I've started creating my own 2 man co-op missions.
Also I'm surprised the OP plays Battlefield solo as you get nowhere in that game without help from squad mates. 99% of the time I get a squad that runs in opposite directions. Especially in conquest where people are coming coming at you from all sides. That's a game that can ONLY be enjoyed with friends.