Hello Jack. Firstly, its great that you have taken the decision to live as a Christian. I had the same issue when I wanted to start my Christian life as well, same like you I was not new to Christianity then. I didn't have any serious Christians friends from my school at that time and I wanted to tell them about Christ and wanted to ask them to stop the worldy things. I did, i tried, and i found out that talking to them about it and praying for them are the only things i could do. Then God needs to work on them. Then the next year i had to change my school and i moved into a school were i got amazing friends from all around the world. And even though they weren't Christians, they never did the worldy things that my friends from the previous school did, like drinking, smoking, sex etc. My new friends were people who i actually could look upto and admire. I thank God for such friends, and i was able to change my school after i took the decision to follow Christ.
What i want you to know from this is that you don't need to worry and get so sad about your friends, talk to them about Christ and pray for them from your heart. Give your sadness to God. Maybe those friends may move on from you due to your new decision, but don't worry, that's only for the best. God will give you better friends. Also, don't completely stop hanging out with them, if they are planning for something which has nothing ungodly in it, then go with them. If you feel something wrong about it, then don't.
Don't worry about how other Christians speak or behave. The Bible clearly tells us how we should behave, follow the Bible.
Keep praying for your friends, i'm sure God will talk to them, maybe through you or someone else.