This is a really tough spot to be in, and I’m sorry that you’re going through that. If I were in your shoes, what I would do is try to have a civil conversation with your friend who is upset, and explain to them that your new friend group makes you feel happy and welcomed, but that doesn’t change that you two are still friends.

If your friend has personal issues with your new friend group, try politely asking them about it, but only if they’re comfortable sharing. If they are, try to find a way so that they can work out their differences either with you or your new friends. However, they might not take it well if they do have issues with your new friends; some personal disputes are bigger than something that can be settled by one singular person, and you need to respect that if this is the case with your friend. From there, I would reiterate the fact that you two can still be friends, even if you are part of a new friend group.