Can no longer form relationships

I do not know how on earth to act around people. My illness is consuming 95% of my life and I do my best to keep it hidden. I don't want to talk about it at all but it's the sole reason I am not able to maintain authentic relationships. I simply act happy towards everyone until I go home. This pressure of just acting all the time has cost me my best friend and has completely thrown me. I can't be myself around others - it simply wouldn't work and I'd b the biggest bore and burden on their lives. No matter what I do I don't want to do it. My best friends just asked me if I wanted to do a weekly class and even though I can't because of work commitments I would panic because that means I have have to think of something to talk about every week with that one person whilst avoiding what is all my life at the moment - anxiety. The comment that I received from a friend on the weekend is still reeling havoc over my mind. (The implication that I do speak about my illness) because I know that to that one person I have probably spoken about it properly once in a year. This makes me want to say nothing in the future because to me, that also being one of my few close friends is saying nothing at all. I can't just speak about my life without thinking what I'm going to say or I know I'll regret opening up like I am right now. I don't enjoy friendships like I know I would if i wasn't ill. I'm scared to become close to people on the basis of how I am with them in general (happy and easy going) because that's what lead to the ridiculous amounts of pressure that destroyed my relationship with my best friend and I am putting every stop sign up to ensure this doesn't happen again. Equally this makes me fear they feel pushed away so I feel the need to explain myself but I don't want to explain myself because I'm never understood and I'm left reeling in frustration. How am I meant to proactively move on with all of this in mind? It feels beyond impossible and any judgements on me feel wrong immediately because no one can begin to understand how I work because you would need a week of me explaining myself just to get a small idea. It's all the more frustrating because if I felt like I had the choice I would be exactly how I'm acting but I simply can't handle the demands because I'm not sure how to express myself because I'm embarrassed and vulnerable and don't want other peoples incites or judgements on this. The countless amounts of situations were people have mentioned mental illness to me and I've made out like I have no idea because I have no ability to communicate on a way that people would even believe I have an illness.

It's a vicious circle that I honestly have no idea how to break away from and have no assistance because of so many tried and failed times

Thanks