Search Results: asking a girl to prom

Basically it's been 7 months since we broke up and I was convinced like 3 months ago I was over her. I stopped thinking about her I thought about other girls, I was with other girls and my ex never crossed my mind as someone I wanted to be with. We have the same friends so we stayed friends and managed to make it work. We still talk but not very much. I've found myself thinking about her again. Especially today. I woke up from a dream where my friend was asking her to prom and I just kept telling myself i just want her to be happy. I woke up missing her like crazy. I can't stop thinking about her and I'm realizing I never got over her. She's been sick and throughout the 7 months I've been calling her asking how she was doing and we had some nice conversations. When she got dumped by a boyfriend I called her to check up and when she got dumped again I called her and we talked and had a nice a conversation. I now realize that I've been subconsciously trying to get her to think I'm the guy for her and I'm always there. I don't know what to do. I miss her insanely right now and I can't decide whether I should tell her I have feelings for her or just let it be and move on. She's perfect, nobody realizes how amazing she is and she keeps getting the wrong guy. I've changed since the break up everyone thinks so. What do I do any advice is appreciated

Here's the deal,

I've been "seeing" this girl (i'm 20, she's 18 by the way, and i will nick name her J) for the past 4 months (October-Now). She has an ex who she said she remained good friends with. No problem honestly. What IS a problem is these points (in chronological order)

-2nd time i ever hung with her, i asked her how her jr prom was. she said "yeah my boyfriends prom was pretty good". i didn't correct her or think much of it. just kinda weird she didn't say "ex"

-on Facebook her female friend commented her photo and said "damn girl lemme tap that ass, (ex) doesn't need to know" and J (girl im dating) flirted back with her female friend

-this caused immediate suspicion, so i confronted her on who (ex) is and she told me (ex) is her ex boyfriend and they remained good friends

-i decided to check out (ex)'s Facebook. His relationship is still listed as "in a relationship" (since the time they started dating back then too)

-Additionally I noticed, on his time line, mid November he posted a "Life Event" which was "Met J"

Now this is weird, why would J's female friend jokingly try to make (ex) jealous? after all, it says he's in a relationship on FB. So either he's dating a new girl, but still has feelings for J, or they're still dating?

Here's what makes me think they're not dating
-A month ago, J told me she told her parents about me. a couple days ago i clarified by asking "they know we're dating right?" and she said yeah.
-before J met me, she hooked up with another guy (and obviously they didn't work out)

Anyway I was thinking about messaging (ex), and this would tell me what's going on completely. something like

"Hey buddy how's it going? Listen buddy I have no problem with you and J being just friends. Just wanted to let you know she's been seeing me now for the past 4 months. Again no hard feelings, just letting you know"

Thoughts on if she's a cheater, or if my message is a good idea?