It is very possible that your original group of friends is not a bad bunch, but that they feel threatened by your new relationships. The way they are reacting is not the healthiest way of dealing with such a situation, but it is also not beyond the pale of normal behavior for High School age children (I have to assume that Shopping613 is right about the age).
I do not think you should be burning bridges just yet. Talk it over with your “old” friends. If they are unforgiving or issue an ultimatum (“it’s either us or them”), let them go. You should never allow someone else to control you that way. If they understand, and it seems that they just need to be reassured about their own standing, they are still your friends and you should not leave them.
Most importantly, I think you should discuss this with an adult who knows the people involved. Maybe a teacher or principal can be helpful in sorting out what’s really going on.