LDR across half the world
Break up supposedly a year ago
You not meeting her
Him being shady
Girl, hate to say it, but you're his side-piece. The distance between the two causes visits to be as seldom as once a year (of which you know, maybe half a year). Her not booking a room in another town who knows how far away is ridiculous. she doesn't know abt you. If she did, she'd never be comfortable assuming she could sleep at his place. If she would be an ex and they were still friends (what is very possible if a LDR fails), there is really no reason to not introduce your partner of 6 months. You're not a fling at that point. You live nearby, so why werent you introduced? He waited until she was asleep to contact you btw.
If I were you I'd contact the "ex" somehow claiming it was unfortunate you couldn't meet her as bf always speaks so highly of her. This way she also knows whats going on if something's going on (what I'm 100% certain of). You can also go the honest way and ask your bf to clear up tue shadiness and decide if you believe him. That's your decision tho