I've NC'd but am a regular poster here, and have started a good few lighthearted pointless threads, I'm afraid this one is decidedly more serious. 
It is long but I don't want to dripfeed.
I will try and keep this as brief as possible, thank you to anyone who replies - I really need some advice.
I have been with my DP for four years. He is the kindest, funniest man I know and my soulmate.
About 6 months into the relationship, I found some pretty flirty messages between him and a woman at work. I told him to stop, that it was disrepectful. He promised he would.
About another 6 months after that I found some more (to the same woman) and hit the roof. He said he would never do it again and just felt bad for her because her DH had recently died, but that he would stop.
About a year after that I found the same sort of messages to the same woman. I was devastated, I left him, lived at a friends,he was inconsolable. We worked through it and he has not (to my knowledge) text her again. Let me be clear - They were not 'Oh my god they are fucking' messages, more silly, flity ones. Stuff like 'Do you want soup?It's upstairs' - 'Only if it's as hot as you' 'I've got new uniform' 'Oh I've always liked a woman in uniform'
God reading that back it's so shit.
He changed the settings on his phone so all messages immeadiatley came through to the ipad I own, let me go through his phone if I wanted to, etc etc, and was by all accounts determined to show me he wouldn't do it again.
Anyway, we got through it - Been together about two and a half years at thsi point.
About a year ago, almost to the day, I found a weird blue pack of pills in his bag. They were open and a few had been taken. He at first said they were nothing, just headache pills. I didn't believe him so looked up the name of them. Obviously it was viagra.
I confronted him and he 'came clean' and said they were for his boss (He part owns a garage with him and tbf they are very close)
After I asked why the hell he would pop a few out of the packet and give them to him just in his hand, then keep the half empty pack himself, he said it was because his boss didn't want his wife finding the pack and he would pop them just as he got home. 
After I pointed out that it really wasn't a big deal, that ED is really quite common, he said that this boss was too embarassed to go to the doctors.
I told him I wasn't happy with him getting them for him (He said he got them from a bloke at work) and he agreed he would stop. A few months later I found the same blue pack in his bag again. I again told him this was dodgy as fuck and to stop. He apologised again, was really upset and said he would tell his boss he couldn't get them for him anymore. When he came back from work that day, unprompted, he said: 'I've told * I can't get him his pills anymore as it's causing me and LyingDP some problems' He said his boss was fine with this and that was that.
A few months later I was in our house at the top window when he pulled up outside. I saw him sitting in his van, take something from his bag and put it behind the visor. He came in and I made some excuse to go outside. They were viagras. It came out that (of course) they were for him and he had just been too ashamed to tell me. He was bawling his eyes out.
I pointed out to him that, having seen my calm and reasoned reaction whe I thought his boss was taking them (nothing to be ashamed of etc), he had no reason to keep this from me.
We have a very open and honest relationship, our sex life was fine. He said a few times he hadn't managed to get it up and he was embarrased.
I am 10 years younger than him and he said he felt ashamed. (I should point out at this point he was drinking about 2-3 cans a night)
We went to counselling. He stopped his drinking. We cried and he said he doesn't know why he lies, just that he doesn't think. I don't think it's malicous. I think he genuinely is a people pleaser and doesn't think of the conesequences.
As part of the counselling, he wrote a kind of 'pledge' that said:
I promise to be truthful and honest with LyingDP, that I will not lie, No matter how big or small and signed and dated it. He carries it around with him in his wallet.
I made it very clear throughout all of this that were it to transpire that he'd lied to me again, no matter how big or small, I had no choice but to leave him. He agreed.
That was a year ago.
We muddled through and I can honestly say we are the best we've ever been, and I have been the happiest and safest I've ever felt.
Cut to today and I don't know what to do.
A week ago we went to a restaurant for our anniversary. He said £40 was through tips at work that he was putting towards it.
I had a pushbike that he kept at his work that he bought for me about two years ago. I don't use it.
My sister (who's DH works with him) mentioned 'Oh, my DH says you've sold your bike?'
So I asked my DP about it today, expecting him to say he hadn't and it was crossed wires.
He'd sold my bike, and, so he said, had used the £30 (???It was a nice bike) to go towards our date night.
He told me he had got all that money from tips. He said nothing about selling my bike or getting the money from it. I don't know how he was going to wriggle out of it when I inevitably asked for my bike.
Had he of asked me if he could sell my bike, I would have said yes. He knows this.
He lied again.
Please help me. I know all on paper this looks awful and I have no doubt what many will be thinking. Imagining my life without him brings me to sobs. I don't know where to start.
If I don't leave it will be succumbing to a relationship where, at a rate of approx one a year, i will be deceived, whether big or small.
I don't have a choice, do I??