Long story short: we have been meeting each other for a while for semi-professional reasons, around two years now, although we only got close in the recent months. We have a very strong group of friends thanks to which we interacted a lot recently.
A job-related difficult situation arose recently and we have been extremely supportive to each other. We talk for hours at night about what's troubling us, we worry whenever one or the other is not in a good mood to extensive lengths. If she wakes up before me she always says good morning and ask me how's things.
I always thought of her as "way out of my league", and for this reason didn't even approach the concept of a relationship until recently: she is very fit while I am on the softer side, and I don't know what to think: she is extremely smart, intelligent, and would never reduce me down to my weight, but I do believe that looks play a part in all of this and honestly I believe myself as quite ugly. All of this didn't deter me from getting extremely infatuated with her, up to the point where she's all I can think about.
We'll have some time next week to be just by ourselves; she hates to trouble others, but she agreed without much fuss to let me accompany her at an important meeting, adding she'd be delighted to have me there.
On one side we have this wonderful friendship, and I'd genuinely hate for it to crumble. We so often joke together and talk about important things and I worry, what if my feelings are exaggerated and they end up ruining everything? Should I just make them quiet down? Of course I am basing all of this on the concept of a sure rejection, but the chance for them not liking me in "that" way is so strong in my head that I am also quite paralyzed.
But then again, a few days ago she re-posted a messenger screenshot in which I appear with a colored heart next to my name, and my brain obviously yeehaw'ed right into over-analysis: wow! a heart!! But.. is it colored because it is secondary, less important to the red one and thus indicating a strictly friendly relationship? Or maybe it's a special color (it does have some meaning for us two, would rather not explain as that'd be too sensible of an information) and thus acquiring the opposite meaning? I guess I would have understood better if other close friends of her appeared in the screenshots, as to gauge whether or not they also had a heart next to their name, but that didn't happen so I'm left with doubt.
Sorry for the rambly mess. Any suggestions and words about how to deal with this are more than welcome.
I think approaching this in a level-headed, communicative way is your best option. Steer clear of openly professing your love for them, just ask them if they'd be interested in going on a date. In your shoes, I'd also make it clear that I value their friendship, and if this isn't something they'd be interested in the last thing you want to lose is a good friend. Feelings happen, handling them in mature way when they aren't reciprocated is the key to not burning that bridge. No matter how bad a "no" might hypothetically feel, not knowing and living with that regret will always be worse. On your other notes about how you see yourself, I've been there too. Clothes that fit and a nice haircut can do wonders (not assuming you don't do these things, just putting it here in case). All that aside, you clearly have a lot to offer as someone they enjoy talking to so frequently. Remember that when you ask, confidence can go a long way.
I think this is really great advice and the most practical approach. It's really hard to tell from this post if she would be receptive to something romantic. Approaching her by respectfully and openly asking if she would be interested in a date gives her the easiest avenue for declining with minimal weirdness, but also unambiguously opens the door if she is interested in pursuing more. Something without a big lead-in, like "Hey, I really enjoy our friendship, but would you be interested in going on a date with me?" should be easy to put out there in a confident but low-pressure way.
Personally, I would struggle to respond on the spot to a big confession of romantic feelings from a good work friend, especially if I didn't feel anything like that. I can imagine responding much more easily to a direct and respectful question about a date from that friend, regardless of whether I want to accept or decline.