I am sorry it is tough . Not always , but men generally are able to detach themselves quicker emotionally and move on .
You are at different stages of the break up and it is perfectly normal to feel upset when your ex is moving on . Especially where this is playing happy families with a new girlfriend and her kids .
It is difficult to think of your DC with them too , but I think you have to accept that it is better for her to have lots of people in her life who will hopefully love and care for her / have fun times with .
You have done so well with your finances etc and unfortunately in some ways this now is the more difficult part .
Whilst it is great , you have had a good co- parenting relationship to date , you need to look at what parts are actually uncomfortable / painful for you now . You have to put some emotional distance between you and your ex now to protect yourself . This will enable you to be the best mum you can be for your daughter .
Cliched but true , you cannot change the situation here - but only your reaction to it . It may help you to try and source some counselling for you , if you haven’t already done so . If you are with a large employer they may have an employee assistance programme you can access .
Above all don’t beat yourself up and be kind to yourself . Relationship break - ups are tough and do take a long time to get over , especially when the relationship was a long one , with DC .
Reach out for support from friends / family if you can .
Look at how you can do things for you when your DC is at their dad’s . That might mean reaching out to old friends where friendships may have lapsed . People have busy lives so may not have time but it is worth a shot .
Take care xxx