How should I act ?

[WhiteTippedCandle]

Married for a number of years.
I need to know what to do in my current situation.

Twice in my life, I’ve known when my boyfriend is about to embark on a new relationship

The first time it was my boyfriend’s new boss, mentionitis, until he broke up with me, for her.

The next time, another boyfriend, was getting calls from a woman at work, on our day off, and he had to answer her.

A few more mentions about her, and we ultimately broke up, and he went out with her. We had been living together, but had briefly split and then got back together.

But both times I knew.

Now attend a sport with our child, and a mum makes a beeline for my husband, always chatting, sometimes to me, but always him.
They could be messaging, I have no idea, as his phone is locked and hidden.
He’s mentioned her.
Ive purposely attended to stop their chatter, but I can’t be glued to him, and they manage to always chat separately.

What to do now? I’ve said nothing, but it’s depressing.

I’ll probably just have to wait and see.
I can’t always attend the sport

Call it out. Tell him your concerns, tell him based on your previous experience you have just reason for being worried about where this may lead while you're not accusing him of anything now you know how these things often unfold.
Alternatively, just watch and wait.

Ask to use his phone and see how he reacts.

Say you really liked that nice mum from the kids sport and you’d like to ask her round for a play date and a coffee as you’d like to get more involved in your kids sporting life and it would be nice to have more mum friends. See how he reacts to that.

I think you should talk to him about this woman. If she is making so very obvious she is attracted to him you should ask him to step back from her and maintain appropriate boundaries.

Thanks for the advice.
His phone is locked and guarded. He wouldn’t let me look at it, or use it ever.

As to speaking to him about her, he would deny and say I’m paranoid,

She has met me and doesn’t care, clearly.

I guess I have doubts still, but who knows for definite.
He takes a lot of care with his appearance these days, and has lost weight.

I can’t attend today, the sport, but she will definitely be there, he was trying to put me off going yesterday.

Because they wait for me to be elsewhere now when they speak, and keep a distance, it’s difficult.

I think I will just have to wait and see what happens.
If they are messaging, I can’t do anything about that, because I can’t prove it.

I’m sorry to say this but all the signs are there that they are having an affair at least emotionally, if not physically.

His phone is locked and guarded. He wouldn’t let me look at it, or use it ever.

This is a massive red flag. You’re his wife. Why is he guarding his phone unless he has something to hide? Why wouldn’t he let you use it? Leave your phone in the car and say you’ve left it at work. Ask him to use his phone to make an important call to work about something. If he won’t give the phone to you, ask him outright why not. You’d let him use your phone, why can’t you use his? If he still won’t let you then you need to sit him down and have a conversation about his secretive behaviour and lack of transparency. Tell him that you have to question why he’s acting weird over you wanting to make a phone call from his phone when you don’t have your own phone available. It’s a perfectly reasonable and totally normal request and his behaviour is shady. It will highlight just how ridiculous his behaviour is and he won’t be able to excuse it.

Ultimately, if he won’t allow you access to his phone, you have to decide if you want to continue to the relationship because if you can’t trust him, it’s not good.

Does he have social media? Could you have a snoop on there to see if they’re interacting online?

Also, sorry for such a personal question but how is your sex life. Is he still interested in sex with you or has that changed recently? How is your relationship in general?

"His phone is locked and guarded. He wouldn't let me look at it, or use it ever."

That tells you absolutely everything you need to know, doesn't it? Whether he is up to anything with this woman or not, there is obviously stuff he is doing that he is deliberately keeping secret from you.

God love you, what a truly sad way to live.
No man is worth this.