I like you but I can't

I'm in a relationship, the relationship wasn't/isn't going so well but we've come to terms at the moment. While the relationship was on the outs I met someone, nothing ever happend, but we both wanted (and still want to) be more than friends/get closer.

However my relationship didn't end so how do I tell this other person, "yes I like you, yes I'm still attracted to you, but we can't right now?" with out sounding stupid or like I tried to play him. To close the door between us but know I can still open it again if my relationship does fail.

He's not comfortable with doing anything while im in a relationship and well really neither am I.

He voiced his attraction and I acted on it, tell him we needed to hang out. So it was my idea to start things up (thinking my relationship was ending) We made plans for this sunday, well my relaitonshp didn't end. and now I've got to canccel on him, and I don't know how to say what I need to say.
So how do i close the door without locking it? Where if we do break up I haven't lost this chance.

You can't keep two guys on the hook at once. It's terribly selfish. Either commit to the man you have, or leave him and start again.

It didn't just happen that the relationship didn't end... YOU didn't do it! So take your responsibilities...

I think you are wrong.You should do compromise with some matters.You should never break the relationship.It will be never never good both for you.

Its stupid too start things while u r not single.
So u should have keep him away till u really was single.

Just be open and tell him how it is.

And if u want to be with him just be honest too your bf.
And break up in a good way. ANd give him time too adjust too the break up idea.
By not showing up in public right away in public with the new one.
And for yourself its good not too jump from dude to dude.

But take a break to heal from it and find yourself back.

I would actually be as honest as possible. The new guy knew you were in a relationship that was on the rocks, right? And he didn’t feel comfortable doing anything until that ended. Well, tell him that the relationship didn’t end and that you are going to sincerely give it a second try. He’ll respect you for it. Whether he was looking for fun or looking for something that could be serious, he’ll know he’s talking to someone who can be committed to making things work out. Stay friends, and don’t be afraid to talk about how things are going with your boyfriend. Tell him you were flattered, but you’re focusing on making things work. Hang out casually (coffee, etc.) in a non-date setting. If things begin to falter in your relationship, you’ll know what it is up with the new guy and it won’t seem awkward if he gets a call out of nowhere.