Help me, please! I have a stupid friendship problem! (It's not super-complicated or anything, I just don't know how to handle this stuff 'cos it doesn't happen to me very often).

Well the thing is that I have a boyf, okay? And he's totally cool... and my ex best friend was having boy troubles at the time. we found out that her ex was cheating on her so she broke up with him. I didn't know that she still had feelings for him afterwards even when he was cheating, so I got a bit carried away, and barely noticing it, started to talk quite a lot about my boyf ('cos he's just so right for me) and eventually she was like, "Shut up, okay? I need a bit of support here and talking about your 'fairytale' relationship with that idiot isn't helping me! have you heard anything i've said over the past week?" and I got really mad at her and completely lost it. Now we're barely friends anymore. We haven't talked for three days and my boyf's being a great help and supporting me but i still feel a bit crap about it all. I'm planning to apologise to her but I don't know what to say without it ending in mais chaos. Please help me... thanks. xx