Hi everyone.
I registered here seeking advice. I do not afford to go to a psychologist yet, and i believe this is the best next thing. At least for some advice.
PLEASE BE PATIENT AND READ ALL STORY:
To put long story short...ish. I will keep it as short as i can. Here goes:
Wall of text bellow:

I am in a relationship that lasts for 8 years. Last Christmas i finally proposed. She accepted but it wasn't the yes that i was expecting.She told me i need to change. I knew my behavior in this relationship was not the best. I am not a bad guy(no violence/drinking problems) my only problem(not to minimize it) is the amount of attention i was giving to her.
Prior to that i was happy that she finally found a girl friend that she could understand and be friends with(she was having some problems around this area). So i didn't suspect anything...Until... Her colleague(we are both in our 2nd year in college<she is 27 i am 30>) started coming to our house to study. The always took long walks and they were talking hours on the phone. One night as i took a shower, i walked past the door to the room that they were staying in studying and heard my fiancee moaning with pleasure. You can imagine i know the sounds she makes when intimacy is involved. I was literally shocked. I didn't know how to react. I didn't say anything and i went to sleep.
I waited, and waited. I then started to put together pieces of information and started to see that my fiancee was rejecting me on some levels, activities together, etc things that i was ok with because i have very little time to spend with her(work & school take all the time that i have). I confronted this part with her(not the moaning one, just the rejection part, and her being distant to me). And she told she wants a break. That my proposal for marriage came very late and it was seen as a forced act.
Next week her colleague came again to "study". So i left my phone at home recording and a different phone recording in another room. I know this was unethical but i had too.
That night was the worse night of my life. While they were in the room studying i was listening to the recording while they were in the kitchen talking. So i found out they had a relationship, her colleague loves my fiancee, and apparently the feelings are mutual. The were long conversations. I deduced the my fiancee still has feelings for me too.
Next day i listened to the recording from the room they spent the night in.
Again moanings and kisses and such...
I found letters of love from one to another. The colleague saying my fiancee is the best and a lot of things denoting that she truly truly loves my fiancee. And a single letter from my fiancee to her saying the she loves her and that she is caught in 2 relationships, one being more important than other.
That night i confronted my fiancee telling her i knew about the letters and i heard the moanings from the 2 nights they spent together. So i knew all about it. We talked. My fiancee said she wants a break because she doesn't know is she wants our relationship anymore, and that the relationship with her colleague as partners was over.
But i continued to monitor, record conversations(phone), and although things on the phone seemed friendly and nothing more, today i listened to my fiancee replying i love you too.
Right now i feel lost. And i feel the urge to kick her from my house tonight when she comes home.
It is true that i made many mistakes in this relationship but she continues to lie to me. I realize that i was ignorant for a lot of time in this relationship, but is my fault bigger than hers? I love her but sometimes i just want to say it is over. She said that i drove her away from me and she found in her colleague the things she missed in me, and that she didn't see her as a girl, but that she felt that she was near a boy next to her. This is also the first relationship that girl has with anyone(she always had her suspicions but wasn't sure to her sexuality, my fiancee told me that she is not feeling like a girl inside, that she hates all the girly parts of her).
What should i do.. Should i trust my fiancee? She still spends a lot of time with her colleague saying that they learn together(which makes sense, but i don't know if it is true). She already told me that she will not give up her friendship with her for our relationship. This she said to me, and to her(while i was listening to a conversation).
I know what i did was not ethical. But i wouldn't have known about this at all. I want to continue this relationship, and as long as i don't listen to recordings i am ok, because things in the house are ok-ish. But as soon as i listen my heart torns apart, again and again because she lies to me. And today i have to proof. Audio of her saying the her colleague the she loves her too. Do i confront again? Or do i wait? I am sure I can move past this, but i have to see that she wants it too. And i do not see that. Obviously she is much more careful with conversations now, and that girl stopped coming to our house because i banned her(it is my house). I know for a fact the my fiancee is not staying with me for material reasons, she can always move to her brother, and she said it to her colleague so that part was true.
I know for a fact the her relationship with the colleague started in november sometime after our 8 year anniversary. (she told me it started after new year. i suppose to hide the relationship at the time of my proposal).
What is her angle here? She still wants me ? she does not?.

Thank you.