Two and two are not adding up here. Something is missing - whether that's gosh you look like a free babysitter, or your ex and I need some "alone" time wink wink, or fiance and you need some "alone" time wink wink, or so sorry you're the odd one out have a weekend with kids as a consolation prize, some combination of all that. It sounds like it's possibly a short visit - "drive for an hour...on Saturday" doesn't sound like the whole weekend, and by kicking LW out of the plans, it does give the impression that they're trying to do the whole thing without her getting in the way.

Queue litmus test of new relationship: is boyfriend willing to back her up when she's not comfortable with the situation, or is he going to cave to his other friends? The answers will be telling.