Am I over reacting

Ive been dating a guy* ( 47) for 7 months. We had been planning on moving in together.* He told me early on that in his previous marriage he had a number of* "unemotional" affairs but he didnt want to do that anymore and was getting counciling.

**** We've just had a holiday together and while booking a tour he became very chatty with the sales woman. He is a very charming, engaging man who easily makes people laugh. I saw that* she was flirting and said to Adam I was uncomfortable with it. He dismissed it and said she was just a friendly outgoing salesperson that he'd connected with.

******* Next day we went back for our tour. I walked in and as way of greeting she said "Wheres Adam" and they continued to chat/flirt. When we left she asked us we wanted to play poker that night but we declined saying we were on our way home.* Again I said to Adam that I thought she was flirting* and he disagreed.

**** Next day i pass him his phone to see a meesage from the shop girl Megan. He had privately messaged her asking how her poker game had gone.
He got very defensive,* saying Im reading to much into it.* It wasnt sexual and thats how people make friends.

***** My marriage of 23 years* ended recently* because my husband left me for his affair partner and I am* aware of being insecure. I never used to be a jeolous person but am now a bit too sensitive .* Adam knows this. He said he didnt tell me he had contacted Megan because he knew I was being jealous and that I'd over react.
**
**** But instead of reassuring me he got angry, went home , sent a message saying he hopes to see.me tonight.
*** Im very confused. I dont think I can have a relationship with a man who openly flirts like that but dont know if im being unreasonable and if its just a hangup from my marraige ending like it did.

Sometimes flirting is just a thing you can enjoy. It makes you feel desireable, desired and good about yourself. Also the other person feels good about it.
I dont personally see what is wrong with flirting with a girl.
If a hot guy came to you and flirted with you a little then youd like that too, wouldnt you?
You cant tell me you would not enjoy it.
And i cant think whats bad about it.

Also actionwise there are some different ways you can handle a partner who is enjoying contact to other women:
1) you can forbid it and be attentive about it
this will pressure your partner make him feel bad and make him keep that from you because he feels you are insecure about it
this will make him used to keeping other potentionally hot women from your knowledge. it enhances his feeling of "cheating" ony ou while he is in fact just enjoying some nice flirty romantic time with someone else.
2) you can enjoy himself with you, being funny about it making him feel comfortable (and yourself too). You can realise that you cannot prevent cheating from happening using prohibition. You could be like "haha that megan was totally over you. Shed totally be cool with a threesome i GUARANTEE IT". If you can speak guy language with him about it, he will feel comfortable discussing this with you. That is where you can realise that he likes other women. You will realise he likes contacting them and flirting with them. He likes the chase. That is also where you can realise that inspite (or because) of that all he chooses you over any women he meets. He chooses you to be with him instead of megan. He treats you as if the other girls cant match up to you.
You have the choice: treating them like that too (friendly but not seeing any danger) or you can treat them like they are a danger to your relationship (and thus they are).

If he cheats on you or not is not the point. However how likely it is and how many reasons you give him to possibly do so are.

Flirting is natural and friendly and perfectly harmless if you are in a secure, happy relationship. It sounds like your issues are your own insecurities that you have not deal with since the fall out of your marriage. You cannot control who flirts with your boyfriend, and neither can he. You also can't control whether or not he flirts with someone else. If your boyfriend wants to cheat on you, he will. You can't control anyone else's behavior but your own. You should consider working through the emotional baggage you're carrying from your divorce so you can learn to see things more clearly and through a less judgmental lens.

Flirting is harmless. Pm-ing the flirty girl later is over stepping the line.

Fair enough, but you were already miffed about him flirting to begin with, so the problem still rests with your insecurities. I'm in no way saying your feelings are invalid, I am just wondering where they are coming from, because you have to deal with the root of the issue if you ever hope to work through these feelings. Jealousy is a completely natural, normal human emotion. We all feel it, we all deal with it. It's OK to feel jealous, and it's OK to admit you feel that way. It's what we do with that emotion, and the reaction we choose to have that can be destructive and unhealthy in a relationship. The only way you can work through this is to acknowledge your insecurities and then talk to your boyfriend about it. If he can't respect your feelings and communicate with you in a respectful, non-judgmental way, then maybe you need to re-evaluate the relationship. If he continually crosses your relationship boundaries, you need to have a discussion bout that as well.