Am I overreacting or is this a red flag?

Honestly? I’d say and do nothing, put it out of your mind. It’s only been 6 months between you. If he decides to go off with this other woman, better to know now. See how he handles all of this, as it’s a good way of figuring him out a bit more.
Also, not saying your insecurity is misplaced (not saying it’s justified either), but if you’ve had a rubbish relationship in the past, it’s bound to have an impact on how you respond to and feel about things with this relationship.

If your DH kept contact with someone who did that wouldn't you think he was being disrespectful to you? Instead of him telling them where to go and blocking?

But he offered to unfriend her, and you apparently told him not to and said 'Do what you want, it's up to you'. You essentially set him a test, without actually telling him it was a test, and are now pissed off because he 'failed' a test when he didn't even know it existed.

Personally, I think the whole dynamic of your relationship sounds a bit unhealthy - you both sound quite intense to me, all this being deeply in love after only a few months and spending all your time together so early on - and I suspect you're both playing mind games with each other, him by telling you about this stuff with his ex and you by not being honest with him and just telling him how you feel and what you'd prefer him to do.

She's on the back burner..
He's enjoying having his ego stroked.. Won't be long til it's more than his ego she's stroking..

I personally would end the relationship. I have no time or patience for this type of thing.

I think he may be seeking to resolve his hurt and prove something to himself, and his ex through the new relationship with you. That’s not healthy. He has not fully processed what happened. It will continue to cast a shadow. Doesn’t mean he is a horrible person but he may not be ready for a relationship.

I would never tell any man that his actions made me feel jealous / insecure or jealous, he now knows he has the ability to do this and can do it again in the future if he wants, you have left yourself open to potential abuse

It may be that he just wanted his ex to feel regret rather than wanting you to play "pick me". That he stayed "friends" on Facebook so that she would have a constant reminder of what she threw away.

If so, it's not ideal that he was playing this game, but at least he was playing it with her rather than with you, and now he's realised what's important and what's not.

Discussing exes as a one off conversation, I get. Continuing to talk about an ex, to your new partner I don't. Unless it's in the context of shared children.
That he initiated a conversation with you about how she didn't get married, is now single and then showed you a photo she sent him as well- it just suggests to me that he's not really over the relationship.

As if you care that she/they will be upset! (If indeed the relatives would be, I can see that she would be, but so what? He owes her nowt). I hope the blocking doesn't lead to more direct non-Facebook forms of contact. But he can block her elsewhere too.

It sounds like you are reacting emotionally rather then responding to the situation. It's not on him to prevent you from ever feeling jealous or insecure. He can't control that his ex is now single and that makes you feel so threatened.

Often those horrible feelings of anxiety or jealousy come from our own issues rather than something external. Your extreme response of wanting to walk away (avoid) rather than tackle uncomfortable feelings points to something deeper being triggered, rather than just this particular situation causing you angst.

He should be sympathetic to how you are feeling but I suspect the strength of your reaction points to there being something else at play here.

Well it sounds like you’ve made your expectations quite clear then. Ball is in his court now. How much grace period are you going to give him?

Well. I’d let it be and not think about it. If he is into you then you’ll have a good relationship and that’s all you need to be concerned about. If he wants to see her then I imagine he will and he would let you know that it’s no longer working out for him. If you think he would cheat behind your back after 6 months then ask why you think that. Gut feelings are valid too. But who could be bothered. It’s not like you have shared finances or homes and it would be difficult to separate. I imagine if he likes you he will keep seeing you. If he doesn’t. He won’t.

Ask yourself if it’s worth the hassle. He’ll keep her as a friend, that much is obvious.

This 👆 💯 👏
It will NOT get any better.
Cut and run like the wind 🏃‍♀️

Its all a contradiction isnt it?

Hes so strong minded and boundaried that hes soaking up the attention from this woman who, allegedly, treated him like utter shit.

And felt it was an excellent idea to show you, his new girlfriend of just 6 very short months, when youd expect someone to be on their best behaviour, messages between them both that only a slug wouldnt realise would cause a bit of weirdness.

I dont think hes a good influence at all I think hes enjoying the drama of 2 women vying for his attention.

This won't get any better op.

MENTIONITIS 😆 👏 💯
I love this! Especially the cheese older than 6 months 🧀 😆 🙌
Don't do the pick me dance.
He's loving the attention. Why else would he still be pals with an ex who cheated in him, and is an ex for a reason. All ego stroking bollocks.
Bin him off, and enjoy your peace 💅

It’s not the fb friends thing, I’m friends with several exes, I bear them no ill will, they’re decent men and I wish them well and enjoy seeing their lives moving on. I have absolutely no interest in getting back either them or even a mild flirtation. I’d be upset about the obvious texting if photos of them though. I’d assume there is something ‘unfinished’ between them.