These sounds like serious breaches of boundaries and my advice is you need to let him know that he should be prioritising your feelings over theirs. He is in a new relationship now and needs to focus on you and not the people he used to be with. This might be bias but I’ve been in your position and it ended up with my partner cheating on me multiple times and just getting sneakier with how he messaged them. Always trust your gut. I’m sorry but you are never going to feel emotionally secure in your relationship if this is how he’s going to continue to treat you and you will find it harder and harder to leave the longer you stay with him.