@Kage This here is the key. If you never specifically said "I'll take them" then you have nothing to be upset about.
I realize when you are new, you don't always understand the etiquette. Saying you're interested and still asking questions unfortunately is not a firm commitment to buy. There is no "reservation." You either commit to buy them, or they are still available if someone else commits before you.
Honestly, all of us have been in similar situations where we were interested in something, but it got away before we committed. Me personally, I'm a big proponent of the "dibs in the thread" then PM process. Whoever posts dibs
in the thread has priority to buy when I sell something. But this is totally up to the seller, and many other sellers don't use this method.