Take a deep breath, let it out. Then another.
Slow and easy.
#1: Stop beating yourself up with the good-grief-how-could-I's. We all have them, and they're invaluable as learning tools.
Only you know what you need to do. Is it better to stay with him and avoid your fear of being alone (even though you cannot see the future)?
Perhaps you're looking at this wrong. What's wrong with some time apart, for both of you to reflect on your lives together? There is nothing saying any split has to be permanent unless you want it to be.
They were all so happy that I had the guts to kick him out this summer (6 weeks) and so disappointed when I let him come back.
Your friends are worried about you, and want you to be happy...but in the end, what they think of you is none of your business. You have to walk in your own shoes.