Reading through the comments here makes one thing apparent again: clear and direct communication about one's intentions can solve all of these misunderstandings. Being upfront will avoid that unnecessary "are they into me or not" over-analasys or missing such more or less subtle hints at all.

If you're interested in someone, go for them! Tell them about your interest. It benefits you both. They'll know, which can help in case they're interested as well, and you'll know what to expect whether they're interested or not. This can also save you a lot of time, heart- and headache.