My husband and I share an Itunes account so use the same email address and password. Our iphones are now connected and we get each other's messages and share each other's contacts. How can we stop this happening?

A couple of different approached:

1. Create a second AppleID for one of you that includes the email address and phone number you wish to use for messaging, but do not apply it to the iTunes and app store (just keep the current one). My wife and I do this and it works quite well. Also allows for easier syncing of Contacts , notes etc. using icloud if you wish to do that.
2. Add additional emails/phone numbers to the existing account and change the Send/Receive settings for Messages. this will not fix the Contcts isues for you however.

Stick with #1 above. Create a unique ID for each phone to use for iCloud/iMessage/FaceTime that will keep your messages and contacts separated.