So a little back ground. My friend Kate(not her real name) and I have been friends since we were 12. My fiance Mike and I have been together for six years this june. Last year when Mike asked me to marry him I was so excited and happy and I asked Kate as well as 4 other of our friends (we've all been friends since we were little) to be my bridesmaids. My other friends immediately fell into the roll of bridesmaids and have been incredibly helpful and are nearly as excited as I am that I'm getting married (I'm the first one of us to get married.) Kate on the other hand, has been less than enthusiastic about the whole thing. At first it was little things like she wouldn't be able to make it to certain functions like my bridal shower because of scheduling conflicts, which didn't bother me at all I know other people have shit going on that is more important than a bridal shower, then she didnt like my choice in wedding location, caterer, cake etc. She literally had a hissy fit when we were looking at bridesmaids dresses because the one I had picked out wasn't "sexy enough". All in all she has been incredibly critical about the whole thing, but I thought it might have been jealousy because she has always wanted to get married and have a wedding while growing up I was kind flippant about the whole concept. -The Current Problem- The past three months I have been noticing that Kate had wanted to come over to my house more. She had said she felt bad about everything that had to do with my wedding and she wanted to be more involved with the process, like our other friends were. At first I was like "awesome, that way I dont have to worry about another bridesmaids dress incident". She started coming over to "help" with the wedding planning but I started noticing something. Whenever she was at the door she would always subtly ask me if my fiance was home and depending on my answer her whole demeanor would change. If he was home she would be her normal bubbly self, but if he wasn't she would get kind of sulky and pouty, kind of like a kid being told he couldn't have ice cream for dinner. I then started noticing that whenever she would come over she would always look really made up. Her hair was always done she was always wearing some sort of revealing outfit and her makeup was always touched up/ reapplied as long as she was here. She then would start finding excuses to come over to my house whenever I wasn't home. She would text me that she would need to drop something off at my house and I would say "sure Mike is home right now" and then I would find out later from Mike that she would be here for over an hour just hanging out. Three weeks ago I came home and she was there with Mike, cooking him dinner. She didn't even tell me she was coming over. And when she saw me she sort of glared at me for a second, like I had ruined something. Saturday night was our bachelor/bachelorette parties. Me and my friends went out clubbing while Mike and his friends went bar hopping. The guys were bored and Mike asked me if him and his friends could meet up with us at the club. I said sure and as soon as they showed up, Kate, who was really drunk at this point made a bee line straight to my fiance and gave him a hug. So that night I dont know what happened, maybe it was the $4 vodka cranberries I had been slurping down, but reality kind of slapped me in the face and I realized what she had been doing. Not wanting to cause a big scene I walked over to her and asked her if she and I could talk outside alone for a bit. She looked nervous but agreed. Outside I basically asked her "wtf are you doing with my fiance?" She broke down sobbing and told me that she was in love with Mike. I started crying too and asked her if that was true why had she been acting on it and trying to hurt me? She stopped crying and literally SCREAMED at me on the street "when two people are meant to be together nothing can stop it." She then went on to tell me that she was a better fit for Mike (that she was prettier, smarter, had a better job etc.) and just down right insulting me. I cried the whole time and THEN while I was fucking sobbing on the street as one of my best friends insulted me, she tells me that she already told him. WTF? Mike didn't tell me anything about it. He hasn't about Kate in weeks,except to comment how weird it was that she wanted to come over all the time. At this point my bachelorette party was over for me. I went back inside the club, ran straight to my best friend and told her that I wanted to go home. Seeing that I had been crying she took me to her house and I told her everything. She was so mad for me she almost went back to the club to kick Kate's ass, which I love her for. I texted Mike basically summing up what I had learned and told him I would talk to him Monday. I shut off my phone and I haven't spoken to anyone and basically spent yesterday nursing a hangover and crying.Mike had been calling all of my friends, except Kate, to find out where I was and apparently he was really freaked out. Today is Monday and I'm going to talk to Mike, but I have no idea what to say. I don't know that he reciprocates the feelings, I don't think he does, but I am really hurt he didn't tell me. I don't even know how to convey to him how hurt I feel, I love him and I don't want to break up with him but this is all really making me nervous about marrying him. As for Kate. Fuck that bitch I'm out. tl;dr: My friend of almost 15 years told my fiance she's in love with him and was planning on "stealing" him from me. My fiance didn't tell me and I'm hurt, I don't know what to do at this point. UPDATE: Hi I'm sorry if this doesn't make any sense I've been drinking. Thank you to everyonewho replied with advice, thank you all I really mean that. You're right that I fucked up and didn't talk to him after I had left I was just thinking aboutme and how upset I was. I called Mike about an hour after I made this post and we talked. I told him how sorry I was for being a shitty fiance because my exfriend was being awful, I offered to go to counceling and work on everything but he didn't want to. He started crying on the phone and admitted that he and Kate had slept together on saturday after our party, apparently he was blind drunk and thought I had broken up with him. That part is my fault, I know. So now I am single and I have no idea about Kate. Thanks again.