My cousin (25F)فنcked up the surprise birthday party I (26F) threw for my boyfriend (26M)

I (26F) am a very sweet and caring girlfriend. My boyfriend Matheus is turning 27 in April and we've been dating for 8 years already, I am 26 and will be turning 27 in June. At first I thought to throw a surprise party for him, he loves surprises and I really enjoy throwing surprises, my family and friends are accustomed to my surprises. Unfortunately, because my surprise birthday party for him got ruined, I have been crying nonstop for the past days as this was the birthday present for him and I spent a lot of effort planning it. I'm not sure what to do now because I can't let him spend his birthday without a celebration. I really want to know what to do now, I could really use some help. I didn't tell him about the surprise party and he doesn't know anything except that I wanted to take him out to eat at a nice restaurant. I had told him that I had decided to cancel the dinner plans for the two of us as I was too tired to prepare us a dinner, he agreed and said there was no problem and he understood my reasons. I told him it was better because I was too tired and stressed. I was going to surprise him to a party at my house with all his friends, my family and his family. But my cousin ruined everything. He was supposed to arrive at 7pm, all my family was there, his family was there, his friends were there too, everybody was there and I was waiting for my cousin (she is also invited to the surprise birthday party). She was supposed to bring her boyfriend with her but she just didn't bring her boyfriend and I didn't say anything because I didn't want to ruin the party myself and decided to let it slide as long as she didn't tell him anything. But she just asked me if she could bring her boyfriend and I said yes as long as she doesn't say anything to him, she said she wouldn't and promised she wouldn't. Well, she lied, she texted him saying she wouldn't be there at my house and said that our family was throwing him a party that I had been planning and all these people were involved. She said she wanted him to spend his birthday specially, with the people he loves. Well she lied. When I saw her text to him, she didn't delete it and I saw she had texted him saying she wanted to ruin the party and wanted him to spend the rest of the night with her and she said she wanted to give him a surprise as well, a surprise BJ. I wanted to puke. I wanted to throw up. She is disgusting. I really hate her for doing this. I was never close to her, we never got along and I hated her. Now I hate her more than anything! How gross is that to plan to give a BJ when the birthday boy is not even her boyfriend and is already in a relationship! I hate her. I hate her. She was just mad that I got more attention than her on my birthday when I turned 18 and had 500 guests at my party. That was 8 years ago, what a bitch. Anyway I saw the message and I had to delete it before he saw it. I was just in time because he was about to see it but fortunately he received a phone call and he answered it and I was able to delete the message. I told him everything and he didn't believe me, said that I was lying and I've never spoken ill of my cousin before and he knows we are not close and he knows we are not friends but he was mad that I was trying to ruin the party. I was not! I was just trying to tell him the truth! He didn't believe me! I really don't know what to do now, now my cousin is really upset that he didn't receive her message. I told her that I had deleted the message and that he didn't believe me. She said she was going to tell him herself but I told her no and she didn't. However she decided to leave the house with her boyfriend saying "I am not going to spend my Saturday with people that I don't like". Well that's good but now my boyfriend doesn't believe me and he is so angry at me that I am almost crying now and my surprise birthday party ruined and now I don't know what to do. I really don't know what to do now, I don't know how to make him believe me, I don't know how to make him know that I am not lying, I don't know what to do as he is very angry. Please help me! What should I do?<br><br>Update: I'm really sorry guys for not answering all your comments, I was really busy (I was crying and I had to call my boyfriend and then my cousin and my aunt and uncle and everybody!) so here's the update:<br><br>My boyfriend didn't believe me! And he is still being very mean and rude to me and he got really angry saying that I was trying to ruin everything and he didn't believe me and he said he was going to my cousin's house and I was asking him "where are you going" and he said "I am going to your cousin's house, I am going to ask her if she is in love with me or not, if she wants to fuck me!" then he left the house without saying anything and then he went to my cousin's house, I felt like I had been punched in the gut, I was so hurt, I was so hurt that my boyfriend would say something like that! I started crying and I don't know how but I ran after him and ran to his car and I wanted to stop him but he was going to fast and then he left! He left! And he said he was tired of trying to get along with my family and that he was going to go to my cousin's house and then he left! I cried! I was so hurt by this, I can't believe he left and said that he was going to fuck her! I don't know if he actually did but he said he was going to fuck her and I don't know what to do now! And then I called my aunt and uncle and told them that he didn't believe me and they came to my house and we talked for hours and my cousin said that she would rather die than sleep with him and that she didn't send the message and that she would have never sent such message. After awhile he called me saying he was at home, I asked him "which home?" and he said "my home". I asked him "is it your home or our home?" he said "it is not our home, it is not my home anymore, you did something horrible, I don't know if I will ever forgive you". I asked him what I had done and he said "you ruined my birthday! You said that your cousin wanted to fuck me! You said that she was in love with me! You ruined my birthday! I don't know if I can forgive you!" I said it wasn't my fault, that it was just an accident but he said I ruined everything and didn't want to talk to me anymore. I called my aunt and uncle again and they said they were going to talk to him but he didn't answer. I'm so hurt and I don't know what to do, I was planning to get engaged to him, I have the ring, I was going to propose to him tomorrow, but now I don't know if I can handle this anymore, I don't know what to do, I'm so hurt, I was so hurt by this, I don't know what to do now. I am so hurt! I don't know who to blame now, my cousin or my boyfriend. I don't know if I can forgive him now as well. Please help me!<br><br>Edit: I can't believe this, I just received a message "I'm sorry for everything, can we talk" it was 3am, I was sleeping, but I woke up and checked my phone, I just hope he is not drunk and that he is actually sorry. I'm going to call him and talk to him, I'm just hoping he is actually sorry for what he did and said, I'm really hoping that he actually apologizes and not just says that it was all a joke, I really hate it when he does that and I want him to understand that it wasn't a joke and that what he said and did really hurt me.