Moving on from losing two close friends this year, what can I do to stop missing them so much?

Time is the only thing that'll make you miss them less and less often. I found that it helps to talk about them with their other friends or family members. I lost a close friend 7 years ago, the first few months were rough, but we were in a tight-knit group with 5-6 others that worked as a good support network. Since then, we regularly talk about him, laugh about things he said and did, and speculate on what he'd be doing with his life today. We're doing things together all the time, but we schedule "[His name] Day" once a year around the date he died. We drink, play games, laugh, and bring up some fond memories. It's just a day to shoot the shit and make sure we don't forget him. I still miss him today, but now my initial thoughts and memories are ones that make me smile and laugh, rather than sadness that he's gone.