First step is to accept, acknowledge and give yourself permission to feel that way.
(my personal blog has a lot regarding my sudden and unexpected anxiety attacks and jealousy this last winter on account of a similar, less significant piece of info regarding my husband-and how I got through it).
The next step is that you have to make it a responsibility to own your shit and he own his shit.
Seriously-not a healthy relationship if he has an open door to lying to you on account of ANYTHING-including fear.
The past is the past-but today has to be used to build the future.
I read a quote-and it goes for men or women-
"Don't punish the man in front of you over the actions of the man before".
He's punishing you (and himself) for past women's shitty behavior. Not acceptable.
Good to reassure him of your love-but he needs to come clean adn deal with his lying issue.
TAKE TIME OUT FOR YOU. Seriously-find what makes you happy-and make MORE TIME FOR IT right now.
Write-you have no one you can talk with that understands-write. Write the hurt, the anger, the fear, the everything.
THat's where you start in dealing with those emotions.
Which-by the way-aren't enough info to define if you "can do this" or not. You've been doing it-so evidently you can do poly. But, your internal weather (emotions) are signalling that its time to make some changes to the situation.
Not a bad thing-just a growth thing.