@Atrocha,
Quote:do you think I have the "right" to ask him to block her on facebook?
Sure, you have the right to ask. Just as he has the right to refuse. Or the right to agree but then not do it and lie to you about it.
Personally, if his relationship with her makes you uncomfortable, if he truly loves you then he will block her without much thought. But I think the two of you need to talk about WHY he went out to dinner and shopping with a woman after 4 years with you. That should be a red flag to you about the state of your relationship. Red flag number two is that he so easily lied/kept secret this "date." Relationships are built on trust. At least the long lasting ones are. Sex can be hot or cold for periods of time. Arguments are going to happen. You will be upset at each other now and then. But without trust, do you really think you can stay together?
In any case, you need to talk about the WHY and how he can rebuild your trust, otherwise this could happen again.