I feel like I did start to get emotionally attached during my deep conversation with his friend
Not to belittle your very real and valid emotions, but you only feel this way due to youth and hormones. If you distract yourself with studies or hanging out with best friends you aren’t attracted to for a day or 2 you’ll cool off so to speak.
I would participate in whatever plans you have already agreed to, but use that time as an opportunity to declare you do not want to escalate the relationship with either friend so you all remain platonic at most. Tell your unrelated friends who will be there this is your intention so they can help keep you on track.
If they get salty tell them ‘this is why: I want friends, not drama. Can you be that for me?’. The answer tells you who you should friend or avoid.