If there's anything that I learned from my ex-girlfriends it's that being too attached and jealousy never works out. If she's mad that you're talking to your ex, dump her she's too immature and isn't worth the trouble. I honestly don't get why girls/guys get mad when you talk to their exs.
1. they're exs for a reason
2. if you need assurance in your relationship then something is wrong (trust, bonds, etc)
3. grow up