I think my first two passes are okay. While I have points, I don't have any good suit to show, and I can't call NT with a singleton in their suit. The problem therefore arose after east's double. At the table, I thought that since I have 5-4 in the majors and 10 pts, it's possible east has something similar in terms of strength and shape. So, he sees shortness in their suits, but hasn't enough strength to TO double and hasn't a good enough suit to overcall with. Then, after the opponents keep mucking about, he sees an opportunity to try and get the partscore, as he estimates we have roughly the same amount of points and a good fit in at least one of the majors.
So, I took the double out to 3S, which was most likely the reason he stood up and left after the opening lead. His hand was this:
So clearly he meant the double to be penalty, and was annoyed that I could think otherwise. Seeing as he was advanced and I am not, I'm guessing he's right, but how could I have known in advance?
Thanks.