It depends on why you don't necessarily see yourself marrying him.
Personally, I don't get into a relationship with someone unless I think we are potentially compatible for life. Of course there's always room to be wrong anyway, but there are some basic things that are important - for example: world views, preferred lifestyles, whether or not children are wanted. If I know I would be unhappy say... never traveling the world, then I won't start dating someone who passionately hates travel. Or if I did, because of our connection, I would talk to them about it first and see if they could see themselves changing or allowing me to on my own.
However, that's not how most people do relationships and it doesn't necessarily have to be. We all change and go through different stages, most people go with the flow and if they really enjoy someone's company go for it without deep life-long consideration. It can just be messy and sad, to build such a strong connection with someone and naturally be compelled to want to keep it going, but fall apart over some point of incompatibility. Learning about yourself, what you really want, when to let go and how to move on in the direction you want to be going is all part of that though - for a lot of people it's necessary for successful future relationships. For others it was just lost romantic time where they weren't meeting other people instead. And then a third category still has completely wrong ideas about what they have/need and throw away something good.
In short, it's up to you and what you feel is the best for both of you.