So I met my girlfriend in October we had been great up til March she started caring less about how I felt and I thought I was the problem. If I showed up with flowers she would get mad and when I needed reassurance she would be like I don’t know how to. Although she had seen me cry a lot in front of her she just got mad at me. So soon my friend confessed she likes me knowing I’m in a relationship and I did my best to avoid her since I saw her every day. Although she was still a friend I tried distancing myself so she would lose feeling. One day she saw me breaking down because of my girlfriend and I saw the reassurance she gave me and love. I ended up kissing her not realizing my mistake til afterwards. Soon I can’t get away from my friend I notice I didn’t like my friend but the love she gave me I was wanting it from my girlfriend instead. I noticed with my girlfriend she started giving me the love I desired after a couple of time of crying in front of her and I talked things out more with her so we are in a good place. How do I tell her what happened without her leaving me? Cause I love my gf more than anything I want to tell her but I don’t want her to leave. The friend recently texted me and told me about a secret relationship with her I denied her and have told her many times I only need my gf. Now the friend is threatening to tell my gf what happened between me and her while the friend is keep texting me reasons to break up with my gf. Even though me and my gf have our ups and downs I still want to try with her and no one else. I don’t care if my friend says she can treat me better I only want my gf. Since shes threatening to tell my gf now just cause the friend wants me all to herself. Does anyone have a clue what I should do? I really love my gf and want to stay with her 
That sounds really difficult, I’m sorry it took a little while before your girlfriend was able to give you the consolation and love you needed.
It’s really awful this friend is in a sense blackmailing you. I’m disappointed they would risk the friendship that way, but it’s also difficult once a line has been crossed.
My personal opinion would be to have an open and honest conversation with your girlfriend.
Starting from expressing how you felt in the beginning and what you needed at the time, then explaining what happened and that you are sorry for hiding that and finally that this person has been contacting you. You could ask your girlfriend then how she feels and what she would need from you. Unfortunately we can’t make someone stay in a relationship if they feel trust us broken and that is a part of being responsible for our actions. But there may be the chance she is willing to try keep communicating open and have a discussion about how to move forward.
My thoughts are that secret keeping is a dangerous minefield. It’s worse when someone finds out that you’ve been hiding something from them through someone else.