should i date this guy who was previously in a 3 year long relationship?

Well there is this guy I have become close friends with. When we first met, he was interested me while he was on a break with his girlfriend, but didn't pursue anything because he didn't know if he wanted to go back with her or if he should go after me. Long story short, I dated another guy, and he went back to his ex. I broke up with my boyfriend recently and then I guess he started liking me again. Then he broke up with his girlfriend. Now we're a thing without a title, but I can't help but think he's going to go back with the ex eventually. I mean 3 years is a long time: a lot of moments and experiences with each other. It's kind of weird to be the girl after that relationship because I will always be wondering if he wants to go back with her or always be worrying that I'm the girl to pass time while he gets over the resentment of what she did while they were on that break from their relationship.

Should i continue things with this guy and see where it goes and how it'll be and risk getting hurt? Or just find other options and move along?

Yes, it's possible that he could go back to his ex. However, he could choose not to as well.

What were the reasons for the breakup?
How long ago was it?
What is your current "thing" with him like?

well their other couple friends broke up too. So they were all friends with each other. Let's just say, his ex and this other guy were comforting each other's ex's while doing each other behind their backs.

it was a year ago when they were on that break when he first met me. He finally explained to her his feelings of resentment and everything and broke up about 2 months ago.

as for this current thing, we hang out almost everyday.

its like boyfriend-girlfriend relationship but just without the title for now.

That sounds like a messed up situation.
Let me see if I get this straight.
A was with B. C was with D.
Then both couples broke up.
Then A got with D and B got with D.
Is that right? Or are there more letters involved?

Was your current guy one of those letters?