Can anyone help me understand why I feel a little bit bad about this relationship?

[50notNifty]

Married almost 20 years, wasn't great with hindsight, and "D"H eventually had an affair and left about 1.5yrs ago. Teenage children who have stayed with me, he takes very little to do with them.
After almost a year, I met someone...totally through chance, friend of a friend. Took it very slowly but I'm very happy with him and it's going well. Hardly any interaction with my teens as I think it's too soon, but they are aware I am "dating" and we spoke about it a lot to make sure they were comfortable with it.
We've kept it quite low key mainly as exDH can be quite volatile, but I do feel I'm well within my rights to be seeing someone I'm so happy with.
I'm tentatively optimistic for the future for the first time in ages. However I can't shake the feeling I'm doing something wrong!
Wondering why I can't fully relax and enjoy this?

You deserve some happiness and you're obviously taking it steady . Just take your time and trust your gut xx

Because deep down you don’t think you deserve it, that it’s all going to mess up and people will know you failed.

You do deserve it. Just enjoy it day by day and don’t think too much about the future 💐

Probably just a hangover from being married for 20 years! It's early days so just take it slowly and hopefully that 'doing something wrong' feeling will fade. You say your ex can be volatile, is it perhaps an underlying feeling that he might kick off and be unpleasant when he finds out you're in a new relationship?

It's the mental baggage your carrying, your worries about the kids, the potential behaviour of your exH...........it all adds up and I think the brain has a natural tendency to be slightly negative about things (self preservation?) rather than slightly positive about things.

Perhaps rehearsing the arguments you going to use with you exH might help (write them into your notes on yr phone?) - literally practise what you're going to say and the tone in which in you're going to deliver them to yourself?

Enjoy your new relationship; embrace it, introduce him to the kids etc. You're only here once. Embrace life.

Thank you all!
You're all telling me what I'm telling myself, but it won't go in!
If I was talking to myself as a friend, I'd be cheering me on (my friends are delighted) but I'm feeling unsettled (although very happy at the same time)
I suppose it's uncharted waters and I don't know how things will move forward.
And yes @Endofyeari think he probably will kick off...not that he has any right to, but I think he will.
@NotnowNanettei don't mind what people think, I know I'm not doing anything wrong but I still feel guilty!

@FlamboyantlyIncognitoi definitely tend towards the pessimistic...i can see all the potential problems...not with the guy but with the situation!

I would agree with other posters maybe a hangover from the previous relationship.
Maybe an idea to inform your ex if he does not already know and introduce your children so that they are kept informed.