Im in an open relationship with my ex and sometimes he assumes im upset or angry it makes him take a step back from getting back with me. what can i do to reassure him that im still the girl he loves?

If he is assuming that you are upset or angry when you are not, then you should talk to him to find out why he is making that assumption, and you should explain to him what is really happening. Misunderstandings, in general, are resolved by communication.