Cheating?

[QuirkyTealKoala]

My partner had 2 phones. The other is just a Nokia he wanted to start using to spend time with the kids and not sit on his phone as much. He used it a few days then left it at work. Fast forward 2 weeks I've found out he's been talking to a 'friend' (has a partner too for context). But every other day, he swears blind it was just hey you ok? I don't like this girl because he tried to sleep with her previously before we were together (at that time he was trying to sleep with anyone as fresh out of break up) and she has said horrible things about me, so they stopped talking, his previous gf didn't like her and didn't like him talking to her. He deleted all texts on the other phone and I keep finding out more lies, for example, the morning I found out he had been texting her he told her not to respond to me and to this day she hasn't, he said he didn't do this then admitted he did. He then said it was one text and call and regretted it instantly, turns out it was texts around 5-6, it's now progressed to talking frequently and telephone call. He swears blind he has no feelings but I just think I don't even text my best friend everyday? Then to come home and look me in the eye. I've told the boyfriend and he's completely ignored me! Also found out he was saying to his colleagues 'she just can't comprehend I think so highly of her, just like all my other friends'. She also sent a text saying 'how do I know this is you' (implying checking it wasn't me) so she was fully in with the slyness of it all😫 I can't make sense of it all and need an outsiders perspective. Did he hide it because my reactions are explosive? Are there underlying feelings they are trying to pretend aren't there and put it as 'friendly banter'? Helppp

If it was innocent he wouldn't be lying to you and wouldn't be trying to hide his behaviour from you.
I 'm sorry OP but the two phones and the frequent messaging all add up to something going on between him and this woman.

Trust your instincts on this one, I wouldn’t trust him at all, he’s previously tried to sleep with her, and now communicating with her a lot, I doubt very much he’d bother to put much effort into all this texting if he didn’t fancy her/ want attention. He knows it’s causing issues between you and hasn’t stopped, so he doesn’t care or respect your feelings. I think I’d leave them to it and dump his arse.

so he stopped when I found out but ONLY because I found out which is what I'm pissed about!! I think there is underlying feelings and the fact she's covering for him. I asked if they spoke about me (which you would in a friendship right? Especially one you've not spoken to in years) didn't mention anything about me none of what I've achieved (a hell of a lot) just that yeh we were together and she said 'you've been together years now' it's so weird

1000% don't think there's any going back from this

He has no respect for you, your relationship or your children. He is being deceptive, lying and hiding his contact with her. He is your problem not her. Thinking about her and contacting her boyfriend is just a deflection. She knows you don't like her so she is probably thinking I'll have a bit of fun here and piss her (you) off. You are putting too much focus on her, even in your OP.

She is not the problem, your partner is.
He is the one that tried to sleep with her,. He is the one who got the second phone to speak with her. Hie is the one who has increased the contact. He is the one who is lying. He is the one who is discussing you with his colleagues. The whole thing sounds very disfunctional including your communication with each other. You hint that you are explosive about the communications between them and that is not helping. He is baiting you and game playing and you are responding as he hoped you would. If he wants to remain friends with her, let him. Tell him you are no longer bothered or care. Outsmart him. You need to switch the focus to his behaviour, the damage it has done to the trust and the relationship.
This will be affecting your children and damaging them. They are innocent victims in all this.
In the short term I would ask him to leave and give yourself some breathing space. Show him you are serious and not willing to be abused by him. It is emotional abuse. Get yourself some urgent counselling and work out what it is you want going forward. In the meantime just grey rock him, don't react, switch off and just communicate as necessary. If he keeps on, just remove yourself. Don't respond or react as he is expecting. The more he tries, the less you respond. You set the agenda going forward. Let him see his actions have consequences other than you exploding. Concentrate on your wellbeing and that of your children. Let him come to the realisation that his attempts at contacting other women are no longer your concern.

The trust is gone, so your relationship is effectively over.

This is great advice thank you. I definitely know that HE was who owed the loyalty to me and not her- contacting her boyfriend was more of a reaction and tbh she doesn't like me so she is going to have 0 loyalty to me! I'm making myself look a clown by messaging him. It is sly the fact she was sneaking around with him too knowing I'm around. He isn't here he moved out the day I found all this out and will come to help with the kids take them to school etc. he sits and says he doesn't want to talk to her it was a mistake but once is a mistake, twice is a choice. He actively CHOSE to use that phone regularly to contact her. I still have NO idea how she has his new number but again, driving myself crazy over what ifs isn't going to do anything because the damage has been done. He's only sorry he's been caught else he'd of sat down and told me the truth from day 1 and stood on business if it was innocent, he's shown that IF he can get away with it he'll do it hence the constant lies- therefore the trust is dead and gone and will never return because what if his best friend has a stag abroad? I could never trust him after this. Counselling is a great idea!