I don't 'know' you but I have seen your posts before and wanted to send my best wishes to you and to say that I think that you are doing brilliantly. 7 months is no time at all, though in other ways it must seem like forever to you.
Of course you still miss him. For some people it takes a lot, lot longer than a few months to move on from a relationship that they expected to last a lifetime. And the fact that you miss him is a measure of how real your feelings for him were. You can't just make them disappear. Be kind to yourself and let yourself grieve. Look after yourself for a while longer yet, before expecting yourself to be able to get on with life. I strongly believe that the first year is very important in grieving. Once you have moved beyond that then the pain won't go away, but it can be a point where it starts to lessen.
And of course you are 'pretending' during the daytime. It is sooo difficult to face something like this with kiddies around, so that you don't have the luxury of being able to fall apart and express your emotions the way you might otherwise. It's important that you realise this, so that you can try to make time for yourself when the children aren't around, to express how you really feel. Have a friend over for a video and a bottle of wine and talk and talk and talk. You need to be honest about your feelings - if only on MN! It's what we are here for.
Finally, huge sympathy in having a chatty and friendly ex. My bf had to cope with exactly the same thing and he was sooooo insensitive. He'd moved on emotionally, though chose to live near to her with his new partner, and to make himself feel better, expected her to, too. If he was trampling over your garden in the same way that he is trampling over your feelings, you would tell him to tread more carefully, or simply to get off! The plants in your emotional garden are very newly planted and deserve a lot of careful treatment and tlc, not great hoofs marching over them.
Look after yourself, Honey, and take care of yourself. One day he will realise what a fool he has been. In the meantime, don't expect yourself to be cope all of the time. If you feel shite, then say so! Your kids will respect your honesty and will also respect the fact that you are holding things together for them.