I need help,please-possible cheating husband

With no one to go to,with no family or friends that could help,I turn to you hoping i can be guided...
I have always doubted and making scenarios about husband possibly cheating,I have always ended saying or lying to myself that i was just imagining...
Now i am shaking and shivering and after sleepless nights i can just come and ask you for advice and help. I have noticed my husband's phone bill shows calls to an ex colleague(who he initially hired and then helped her in securing a second job) at times when i am not around ...not many,a couple every month..One on his birthday for long 10 minutes...They appear online on online message software almost at the same time of few minutes apart,including early morning hours when he is supposed to be traveling and she sleeping...Ive met her ,went out once as colleagues,i didn't sense anything...his phones are always password locked,by chance i could see he is deleting the calls to her and has no active chats on although i can clearly see him online or "last seen at"...he goes to gym intensively now, he buys new clothes,he goes out with the guys on weekends...he is either too nice with me or accusing me horribly of cheating myself...we have kids,we are both successful in our work....this all crumbles on me and i don't know if it is my imagination or he is just a cheater...I am dying slowly in the past few days,i can't eat sleep and i fight myself to stay composed....i know i have no chance of going alive through this,he would do anything for his kids and deny and destroy me...he is capable he is and the kids are his everything...I need help please...im desperate and cannot even cry...i want to know..i want to escape...but how would i leave if i do not know for sure..In a divorce here i would stand no chance...where to go,i stayed crying in the rain until a colleague realised something is wrong ,I dont know who can help...who can make light for me...do i go to the police,do i follow him,do i run?..Please help me...i see no options ,and i would die if i loose my kids.