Background: I have an old and very dear friend, and we now live in different cities (I moved away for my work). We see each other about six or seven times a year - either she comes over to us for a weekend, or if I'm in our old city on business, we get together for a meal/catch up. We talk often/text occasionally/FB the rest of the time.
We've just returned from a lovely, long-planned weekend away together involving a trip to a city, a Christmas market and a visit to a large stately home. However, my friend spent the entire weekend (and I do mean non stop) texting a bloke she's recently met on some internet dating site. He's already told her she's not his type, but she admits she's obsessed with him. She bought a postcard to send him at the stately home, and even asked me if I would like to write him a short message. 
Unfortunately she has form for this - the last weekend she spent with us, she spent the entire weekend gleefully texting filthy messages to another man who she'd met on a dating site, and then telling me in eye watering detail what he'd just sent her. Every time I tried to change the subject, my efforts fell on very stony ground.
I get that mobile phones are useful and I made a couple of very quick calls over the weekend but out of courtesy, I kept them brief. Am I just hopelessly old fashioned or is it rude to so pointedly ignore your friend/travelling companion? I did find it a bit hurtful if I'm honest.