Capricorn is a very vulnerable sign and a very proud, too, so your Sea Goat ex is most likely to take refuge in work overload or to simply avoid you at all costs, even if it seems ridiculous. Another tactic they can resort to is looking for chinks in your armor and poking you in the soft spots.
Things may go as far as, say, a parental neglect lawsuit if Capricorn sees you turn away from your mutual kid on the playground for the shortest moment. Lucky for you, in another short moment, they would often take the blame and admit they are insecure. The best thing you can do is to offer a helping hand – your Capricorn ex is very likely to accept it.