Am i crazy

Its 4am, yet another sleepless night, here goes.

My current relationship of 3 years is on the rocks. There is no trust. I recently lost my job due to the overwhelming stress of a dying company, a dying child and a dying relationship. We have a terminallly ill son and recently my partner won full costody of her daughter taken by the state from her ex husband. Ive suspected infidellity for some time now and have seen nearly everything but actually catching her in the act. We were to get married in 5 months and i find now that because of the severity of this , coupled with our ill son reaching the end of life expectancy, financial hardships and conflicting parrenting issues, we are both hessitant. I suspect she has cheated with a not so good friend of mine as late as xmas day 2016. I dont know what to do. Early on in the relationship, i emotionally cheated, talking to women online and trading pictures. I regret this, amd i feel it crushed everything she had for our relationship. Simlnce then, things have been on a fluctuating but definate downhill slope. I love her and our children (both children are from her previous marriage, i have none biologically) . I love her but i cannot trust her, i am almost certain of infidellity in her end (odd behavior, sneaking around, finding evidence on her phone and in the house and even on her body (marks ect)). She maintains she has not cheated however in conversations,things are said unnoticed by her that confirm. For me, i cannot get past the fact that not only has she eated ,but that she is covering it up and highly likley with a old friend of mine that is married. Its two fold, the old "friends" betrayal (friemd of 14 years whom we attended his marriage) now in alliance wirh my fiance and involved sexually. I cannot bear the fact of him being at my wedding or even in my life having had his way with her,she is so sacred to me. It seems there may even have been multiple partners for her. Though i made the 1st mistake, i never physically cheated , i swear this. I feel it is a lower level of its own. I am worn, lost and most of all severley hurt. I feel the constamt distance and pain are beginning to chamge me and my outlook on life as a whole. I feel i am becoming more cynical and skeptical of people. I was raised catholic she was raised christian but for a while has been balancing between agnostic and athiest (leaning toward athiest).

Recently as our son approaches his final stages, she has been leaning back towaed realizing religion is not bad and has ordered a devotional bible. I have been non practicing for years and consider myself agnostic. This became more solid when we met. Her and i would talk for hours on many things and led eaxhother to consider what we knew and challenge orbeliefs to understand more. She was the only athiest I had ever kown on a personal level and happened to be someone whom i had grown so close to not only physically, but emotionally. In short i need help, ive never felt so betrayed and made to feel like nothing so badly in my life. Please, help me. Thank you