Have been in an LTR since the last couple of months.Her ex keeps calling/messaging/sending her gifts , he has an idea she is fooling around with me.

They did make plans for an international trip before they broke up. She still intends to make the trip with him and it is for a duration of 10 days.She insists that she doesn't feel the same for him and to trust her.This leaves me with a dilemma.I could

1.I can talk to her about it and soft next her if she is admant.

2.Demote her to a plate.(need pointers for this).

3.Walk away completely.

What would you gentlemen suggest I do?