Many artists have this concern and it is natural for you to have the feelings of jealously when he is with his ex’s. However, the nature of your situation and profession is such that it is likely to keep happening. The work here is to invest your energy in trusting him. You are not going to be able to manage all the moving parts, but you can make a decision about your trust. In this regard keep confiding in him about how difficult it is for you to. Your jealousy can be helped by sharing your concerns and vulnerability with each other.
Finally, you may want to find ways to change how you are thinking directly. For this I’d highly recommend The Resilience Factor. This is a wonderful book about challenging the thoughts that have become burdensome.
Wishing you patience and peace,