Some context is due. We've known each other for more or less 9 years now, from our late teens and now nearing our late twenties. We both lead rather busy lives, so especially throughout the past few years, we tended to fade in and out of each other's lives. This more or less depends on whether we happen to be single or not.
A couple of months after we initially met, during our college years, I did ask her out but she thought otherwise. Nonetheless, we remained good friends, and have supported each other a lot through these 9 years.
For the past few months now, we've been hanging out quite a bit, certainly more than we have in the past couple of years. Perhaps, those initial feelings of so many years ago are resurfacing again -- but I don't know if that is okay, after so many years of friendship.
There are, perhaps, some red flags which I feel I should point out. I have always sought her advice on relationship matters [I am quite introverted and shy when it comes to these matters]. Certain things she says I should look out for, vis-à-vis signs of interest, I seldom see from her. But, then again, I personally think that they are out of her character -- but let's say we don't assume that.
How would you approach this matter, while being respectful to 9 years of friendship and trust?