Why don't you just call it a day and get rid of him. He's cheated on you already and some girl (whether she works with him or not) sending him a kiss is him on his way to cheating on you yet again. Instead of understanding why you snooped he was furious with you. None of what he's done and is doing is a good sign.
You are obviously NOT meant to spend the rest of your lives together so just dump the chump and get on with the process of getting over him and what he's done to your confidence and self-esteem.
He's a douche bag and the sooner you realize that and get out of his life, the better off you'll be in the future.
“The willingness to accept responsibility for one’s own life is the source from which self-respect springs.” ~Joan Didion