does my colleague like me and what should I do?

So I don't usually do this as I'm quite a private person when it comes to this kind of stuff but I need some advise.

I'm a British born Chinese male in my mid 30s and work in on office. I've worked there for a year and recently I've developed some kind of attraction to a female colleague. We work in the same team but on different projects. Even though she's never mentioned it out right I'm pretty sure she's single. The thing is, is that she doesn't have a permanent seat so roughly once a week she ends up sitting next to me. Every time she is there we have some interesting conversations and as we have a similar sense of humour there is always some banter back and fourth and we just tease each other. I can sense some light flirting on her part i.e. acting all cute-like, laughing at my silly jokes and I've tried picking up small details on her looks and habits etc. and commented on these. She's also quite a private person but I've noticed a few times her talking to me about her personnel life and opening up slightly.

What I've also noticed though is that I always instigate the conversations and try to get to know her better - otherwise we can sit there for hours without talking to each other. She also seems to light flirt with others too but not to, I don't think, the same degree with me. When we don't sit next to each other we seldom speak but I always have a sneaking peek to where she is sitting and I don't see her looking back at me. There's sometimes when she kind of walks past me when we are both not at her desks but she doesn't come up and say hi.

I wouldn't say she is the kind of girl I would usually be attracted to so I question myself if I actually do like her but then during the rest of the week and throughout the weekend I always think about her and picture her, imagining what it would be like if she was there with me....I can't get her out of my mind!

I've not taken things to the next level as there was a similar experience in my last job and after 6 months I eventually built up the confidence to tell her I liked her but she told me she didn't feel the same way, even though I was pretty sure we were quite attracted to each other. This left me quite heart broken and took me months and months to get over it.

Therefore this time round I don't want to ask her out or express my feelings unless I'm 100% sure and if things didn't work out it's going to be really awkward in the office. But I really can't tell if she likes me as a colleague or something more and without knowing for sure I'm going to continue having these feelings for her. I know I am attracted to her but I'm also questioning what exactly these feelings are? The thing is I have other female friends outside of work (friend of friends) and even though on the outside they would be a better match I just don't think about them the same way like how I think about my colleague.

I would appreciate some advise from people whom may have had a similar experience or comments from a female perspective on what I should do and provide some advise on my situation.

Many thanks in advance