This dominant has been training me the last five months and we were dating, but we also decided to leave our options open...we've been getting emotional with one another to a point...but he has been scared to getting too close with me because he doesn't want either of us getting hurt in the end.
He's afraid of getting too emotionally close because you guys might get hurt? That's the name of the game. Nothing ventured nothing gained. The only way you avoid getting hurt in relationships is by not having them.

he told me that he dated alot of submissives in the past who had problems and I told him I understand that...he says I am the only submissive who was more stable.
He sounds a bit unstable himself. I am betting that he's not the most emotionally stable and mature fellow. Everyone has baggage, that's the nature of things. But from what you've written, I'm betting he's not really aware of or dealing with his.

Anyways he recently told me his ex came to him for help...and he told me she needed a place to stay, he didn't tell me anything about the situation.
Drama. And more instability. At this point she could be there for any number of reasons. He could have a white knight "let's save the damsels in distress" syndrome. Or perhaps he has issues letting go? He might just want to have his cake and eat it too in the sex department. Or he could just be a sucker, an easy mark.

But all of that is irrelevant. He sounds like one of those people that go through life attracting drama. If you don't mind that, then fine. But as long as you're with him, be prepared to have everything and the kitchen sink start coming and interfering between the two of you.

At the very least, you need to have him tell you the truth about why she's there, how long she'll be there and what exactly is the nature of their relationship. Especially if you have budding feelings for each other. Otherwise you're just half assing it and he's a fuckbuddy dom and it's irrelevent who he sleeps or plays with as long as he's using protection.

He just said he hopes we can still be as we are that he still wanted to be close....he kept saying that...it felt like he was apologizing for something. It felt like he knew something is going to happen...it just confuses me...he knows in the end I don't want something poly..and he knows I tend to be a romantic even though I am a submissive.
Does he want poly? Is he a poly type of fellow?

What do you mean when you say it felt like he knew something is going to happen? Between him and the ex? Or between he and you? Or between the three of you? What did he do or say that made you sense that?

I can understand if he wants to move on but I think he is only trying to keep his options open because he doesn't want to feel emotionally...I have been avoiding him but now he is starting to contact me more...asking if I am all right.....etc.....if I want to talk to him. I just am frustrated and its confusing to know what to do
Again. That fear of getting hurt thing. He might have a fear of commitment. Or might not just be ready for a relationship. But then you don't sound like you're ready to make that leap either. Or necessarily that you want to.

I know, the thing is I don't even feel like talking to him right now because I know something may happen with the girl but I trust him not to, thats why I am submissive to him. I know we are far, and keeping options open...but is a ex moving keeping options open to a dom?
This is why you need to sit down with him person to person. Set aside the d/s stuff and find out the nature of their relationship, why she is there and how long she is expected to be there.

Just because he is a dom does not make him right. He is only human and will and does make mistakes. Just like you. And if you as a person and his sub have a problem with something he is doing as a dom or person, then it is up to you to communicate that to him. And it's his responsibility to address it.