i think both of you should develop good understanding among yourselves and try to know more about each other.what you likes, what he likes what is common in both of you.after understanding each other decide whether to marry with each other because this is matter of whole life.

Definitely talk about this. It may just be as simple as you telling him that you really like him and you like hanging out with him, but you just want to take your time getting to know him more. Little by little and not too much too quick. It takes a lot of time to really get to know one another and even if yall did move into together you would still have to give each other time to get used to each other and develop a rhythm.

Yes, talk to him about where you stand and figure out where he stands and then compromise and get a clear understanding.

Tell him to slow down and not try to play YOUR future with his. Things have to run a natural course and not be sped up by somebody. He may be a control freak or just needy.

Definately tell him.
ive been in that situation myself, and i didnt say anything, and at the end of it, i was stuck between a rock and a hard place; she asked me out, after a week. i didnt want to say no, and hurt her, but i didnt want to say yes either.
telling him asap, and explaining that you do like him, but you want to take your time is the best thing to do.

Honesty is key in any relationship, and I think it's especially important here, because you two don't have a relationship: he has one, and you have one. He's in a serious relationship with the woman he loves, and you're dating someone to try and decide if it's going somewhere. Somehow, you need to get into the same relationship. This isn't only to prevent his hurt feelings if you break up, but he is probably constantly confused and concerned by your attitude towards him. He's probably wondering why you're not introducing him to your family, and why you keep changing the subject when he brings up the future. Even if you stay together, he deserves to be on the same page with you, and deserve out from underneath the pressure it sounds like you're experiencing.

I would recommend that the next time he starts talking about kids or marriage, you tell him something like "let's not pressure ourselves like that. I don't want to rush us and ruin anything. Let's just enjoy all of the phases of our relationship, and really enjoy our time." Even if you do end up in love with him, and staying together long-term, who wants to look back and think "well, we never really had that 'new love' feeling, because we were already looking at furniture!"? Taking it slow isn't a sign that someone isn't good enough for you. Quite the contrary. I think you can gently get him to see that.

Good luck!