Trust issues with new partner

[Wotsitsareafterme]

Apologies if this turns in to an essay. I need to unload. Partner of about 3 months. Everything right now is amazing. He is loving, attentive, supportive, in constant contact, very very affectionate and very serious about the relationship. Sounds good right?
Very early on, a couple of weeks in and when only a couple of physical things had happened I was contacted by another woman to say she had found out he was seeing me and binned him. At that point if he had been dating other people I wouldn't have raised an eyebrow - I wasn't but I would have thought nothing of it. I was also not really invested at that point. I was quite horrified by this contact. Dp has resolutely denied it and stuck to his story even though I have said 'look the poly dating isn't an issue, only lying about it is' he retains his position. I went around in circles with this for some time and think I am left with the choice between turning a blind eye (I would rather I hadn't been informed in the first place) or not continuing with the relationship.
Fast forward to today and dp has been questioning why I don't really trust him 100%. I was quite blunt about the above being the reason. He remains very patient and he has done everything I have asked him to do. He really is a great partner but this thing with the other girl hangs over me. I try to be stoic about it and say this is just dating and not to over invest anyway but he is so keen and very invested in me it's very confusing.
I keep trying to second guess him in a way I wouldn't normally - like is he over compensating etc. Really very confused

Who does he say she is?

If I was going to choose who to believe in this particular scenario it would be very clear to me

Has he given any sort of explanation as to who she is and why she would do this?

Woman he works with whom apparently he has dated briefly earlier this year. She wanted more and he didn't - his explanation. Trying not to drip feed but some of her story is very ropey.

Broken that's my theory too. I met him online so he was definitely actively looking! I checked all the major sorted recently - no profiles. In fact no evidence of wrongdoing can I find at all. He gave me his phone code and told me to look any time I wanted. He talks to me all day and for 2 hours every night on the phone - so I know he's home alone. He is quite emotional about me. He spends every spare minute here and moves mountains at work to fit around me. He wants to introduce our dc - I have said out of the question just now - he said ok when your ready.

3 months in isn't a partner. Take a step back.

He's not a partner! He's a boyfriend who has lied to you. He's shown what he's like really early on - count yourself lucky. And then dump him.

You're right it's not. It's my lazy abbreviating. I would define it as a bloke I am dating

Based on his behaviour so far I'd give him the benefit of the doubt, you have no more reason to suspect he's lying than you do to suspect she is.

Oh really, spanisharmada? Why would she bother saying all that if it wasn't true?

This won't end well.I suspect OP isn't listening though, because he is love bombing her.

Why would she even if it was? Out of care, compassion and loyalty for OP?
Like I said, either one could be lying. Personally I'd believe the one I actually knew, who had given me no other reason to suspect them.

Because jealously is a big motivator. I have hammered him over this. I don't think I would have put up with me recently. Can't help thinking someone with options would have just simply moved on and picked up another.

Ugh he sounds horrible.

What did this other woman say, then? And his response? I mean, did he say he used to date her, but before you got together? Maybe he isn't lying. If everything else is good, I wouldn't write him off.

She said that she had found out he was seeing me whilst she thought they were together. Can't make me - yes that was his response - that they dated briefly in the past before he met me. Everything else is good.

I'd be inclined to try to move on.

It's not the overlap. We weren't exactly together - not making excuses more judging by my own standards. It's the presumed lying. I have been very firm with him that this is what stops me getting serious. I always get the same response from him that he isn't lying and pleads with me to believe him. So we are kind of check mate. I enjoy being with him but I remain a bit meh about getting v serious. It's one day at a time and I fully expect there to be drama ahead.

He is too far into his story to backtrack now. Rather than hold his hands up and confess to lying because he feared losing you, he w