Its real simple OP...Relationships are built on TRUST.

If she can not/will not trust you to go the the movies with an old "friend" then you have a bigger problem than you think.

Does she trust you to go to work, the store, the bar? If you were going to cheat on her I'm sure you have plenty of opportunities.

If she can't deal with honesty and truth, or if she insecure and jealous, maybe it's time for you to have a long conversation with her.....or move on.