Theres nothing we can do to change to the past - i think you need to focus on improving the trust in your relationship, if he's not acting in a way which makes you question his integrity you have to accept what is and make enough happy memories with him so that you don't constantly compare what you have to what he had in the past. Don't let this issue undermine a good thing, rise above the behaviour of his ex's - you have nothing to do with them and neither do they have any right to get involved in your business. The more you avert your attentions to what matters the better i think. Hope ive been of some help. All the best.