Friendships???

I do not understand how friendships work. 

I have just started a new job and I really like one of my new colleagues who is the same age as me and is waiting to be diagnosed with autism. I get on with her really well at work and I have even pushed myself to go to social events outside of work with a group of colleagues which is very outside my comfort zone. We seem to get on really well at work and even at these events but then when I try and message her she ghosts me. I dont understand how to pursue a friendship in less of a group setting and more a one-on-one friend. Like I feel annoying and like I am bothering her because maybe she doesnt want to message me and doesnt see me in that way, so should I just accept she doesnt want that type of friendship and give up or could it be becuase she is autistic and struggling too in a different way I dont relate to?? I dont know if I should just slowly build up the friendship over the group events we both attend but then I also feel like in these events I am clinging to her in desperation in the hopes she will like me. Another thing I feel is jealousy kind of like I get upset when I see she has replied to someone in the group or messaged someone else privately whilst still ignoring me. Like it makes me feel stupid and small because I am just waiting on this hope of a friendship that maybe isnt even coming because she doesnt like me. It feels like I just get disappointed when I see her message other people because I dont feel good enough, like why cant it be me that has a friend? What is so wrong with me ? 

Also whilst we are out in these group settings I feel like everyone gets on and I am actually having a good time but then there's certain people who pull faces at other people or come to me privately to talk bad about someone else in the group and I just don't get it. I just feel so self-conscious and cant help wonder what do these people actually think of me. I dont understand how to navigate that either because I don't want to distance myself in fear of them talking about me but it is really negatively affecting my mental health. I am second guessing everything I do and say and sometimes I shamefully join in in the bad talking about the other people and I feel horrendous because that isnt the type of person I want to be but Im just trying to fit in. 

I really do not understand how to make and maintain a friendship because Im trying my best to put effort in but then Im just worried Im being annoying and Im really paranoid. I am anxious all the time constantly overthinking why I dont have any friends and why I cant make a friend. I just feel like being diagnosed with autism answered a lot of my questions but then also opened up so many more. Why is it so difficult to make friends?