Mrs. TG has some valid points...your jealousy is very likely a contributing factor to these probs Big Bro, but it's surely not the only one or the cause of it all.
The fact that your gal is totally unwilling to communicate is keeping you two from moving toward any kind of resolution. How can she expect you to understand, or how can she understand you, if she says nothing besides "I don't do anything wrong"? That gets you two nowhere...she's throwing up a wall to block communication, and thus a resolution.
I'm sure you realize this already, but you can't expect this situation to get clear up with time. Usually it's the girl who tries to communicate & the guy doesn't say much. I know, I've been on both sides before. Sure, she has this new-found attention from other guys & probably other girls...she's proud, she enjoys it, and she damn well deserves it if she looks as good as you say. But the fact that it's placed a wedge between the two of you makes all that worthless (or it should). It sounds as if she'd rather have the attention of strangers than have a happy relationship with you.
I don't know, maybe she's confused about what she wants right now. But the facts you presented are that you two do not communicate any longer, you sleep on the couch, you're miserable, she pays no attention to you, yet you love her to death and would do anything to make it all work. What's missing? Her willingness to make it all work.
I do know how you feel bro, I've been in your shoes before. That relationship was less than yours...just a year...but this girl started acting more or less the same way. The difference is she finally talked with me and we went our separate ways. I hated that outcome, but in the end it was best for me. Now I'm with someone who seems to care 100 times more than that chick, and we've been together almost 2 years. The reason I say that is both to tell you I've been there, more or less, and that even if you two end up apart, you'll find someone you deserve.
It sucks to say this, but you need to sit her down, tell her she doesn't have to say anything right now, but just listen to you. Tell her how you feel, what you've seen changing between you two, tell her you don't understand but want to, yet she refuses to communicate. Say all you feel you need to say to her. Then, tell her she must communicate with you. Here's the kicker: if she is unwilling, tell her you cannot be with her then.
Only you can decide when you're ready to take that step, but I don't see how anything can improve when she won't talk to you. Yes, people can change, but I think those cases are rare in comparison to those that do not. You cannot make her change...only she can. You deserve more than being miserable, no matter how much you love this person. One thing I feel is for certain, if she will not communicate then nothing will ever change.
Good luck bro.