How to let her know how I feel?

A couple of months ago I go myself a couple of new neighbours. These two girls moved into a 2BR apt. I helped them out pretty much with a lot of different stuff since they were new in the country and so. We then started to hang out. More and more for each day. Nowadays we're hanging out every day and we are like brother and sisters.

The problem now is that i've started getting feelings for one of them. Actually I got them over a months ago but then I found out that she had a crush on another guy so I just tried to forget my feelings and move on. It was, maybe a week ago, when I started to notice something, she called me at 1:30AM and asked if I could make her company to the gas station to buy some cigarettes. I said that I already laied in bed and was just about to sleep. Then she begged me to put some cloths on and come with her(this was weird since she goes there almost everyday and she never had any problems with going there alone before). I put some cloths on and we drove over to the gas station and talked a little on the way over there. Then we just went back home and we said bye and goodnight and I went to sleep again.

Not sure if this means anything but I can not find any other reason than that she tried to show med that she got feelings for me, right?

I really not want to make things weird between us three, cause we have become really good friends, but I also want her to know how I feel.

Any tip on how I could find out how she feels in some smooth way? Do you think the other girl(her roomie) will be jeallus if she and I started to hang out together?

I really got no experience with girls so I don't know how to handle this. She is a bit older to, she is 25 and I 22. Will that make a difference?

Hope you could help me with this!