the man, the fiancée and me

Girls I just need some advice. 
I work with a guy who, from the start I've known is engaged. Long story short we've been seeing eachother for 8 months now and it's pretty serious. I know everyone says to not trust him but we've always been open about how we feel and it's got to the point that he is consistently saying he doesn't want to lose me and if he's still seeing me a year on he will walk out of his relationship as clearly he's not meant to be with her. He's getting married in August and it's just affecting me in every way possible the closer it gets.
Any tips or anything to just help me deal would be great.
As a girl I hate that there is another woman involved however it wasn't intentional and now both him and me are in too deep to let eachother go. 
I just don't want to be hurt as before 😬