My partner lied to me too ... and it is hard it has been almost a year now and I would love to tell you it has been easy but it hasnt.
It will take alot of work on both your parts. As AutumnMaidens said you have to decide if you want to trust him again, you have very right to say 'actually you have blown it I dont trust you and I dont think i ever can' but if you want the relationship then you have to accept it.
Have you discussed the lie ... why did he lie, why did he feel he had to lie and does he understand fully how you feel about it and that lying is wrong.
Once you have these secure in your head then all you can do is give it time...
there will be times that you dont believe what he says and you have to accept you feel like that because of what has happened, and he has to accept that the reason you struggle is because of his lying.
It can be done but there is no quick fix ... I really wish there was.
If you want to talk about it to someone who understands I'm more than happy to chat ... just message me
I hope it works out for you which ever way you go xxx
Laugh your head off, dance in the rain.
Cherish all moments, ignore all the pain.
Live, Laugh, Love, forgive and forget,
Life is too short to live with regret.