Gallen, I had serious lies and a huge breach of trust with my DS1 a couple of years ago, when he gained access to my savings and stole a large amount from me over several months to buy drugs (and junk food). I felt furiously angry, betrayed, desperately upset, and thought my love for him was damaged beyond repair. :( I can tell you these things from my own experience... No 'answers' - just insights I gained that might perhaps be useful...
I needed the 'upsetting' behaviour to stop. While he was still lying and behaving like a dick, there was just no way I could forgive him or start to rebuild trust.
I found I was thinking about it all the time and it was 'colouring' all my interactions with him. I was angry about that, but it was done and there was nothing I could do about it, so the associated anger sort of attached itself to other things instead. I recognised that wasn't fair or helpful, but it took me a long time to be able to stop doing it.
There was a vicious circle of anger for months: I was still angry with him, and he was angry with me for being angry because he felt he'd 'confessed' and it was 'over', and I was angry for him for being angry with me when I felt he should understand and be contrite...
I had to put measures in place to make another similar breach of trust impossible (I changed accounts and put locks on doors). Then I was free from the worry that it might happen again, and could start to feel and act more positively towards my son generally.
It has taken a very, very long time. Almost two years on, I still do not entirely trust him, and I'm not sure I ever will... Something precious was broken, and I have had to deal with a sort of bereavement about that. :( I do now know I love him (again?) though, and I was not sure that I would, so that's good.
He does still sometimes lie. Truth is obviously not as important to him as to me - or not yet, since he is still only 18. It's sad to realise my child doesn't have quite the values I'd hoped he'd have; but it's also an important lesson, perhaps, that he is his own person - we don't get to mould our children as we perhaps imagine we do when they're little!
He is, however, developing moral values that I can respect. He's made some good choices and come a long way. That's a relief. I think one of the worst things about a child breaching our trust is a huge fear that it means they will 'turn out bad' - and it's good to know that they can recover from even enormous mistakes.
Good luck. :)