Most Helpful Guy
At first, you better make sure your impression is fact too. Then if you validate you genuinely don't like him, and you see no possible way to make it work, it is better to be honest. Ofc this doesn't mean to be sharp with him, just not to go with covering up and acting as no problem is there. You two may even work it out together. In the end honesty is the best for healthy relationship. As it sounds, it may be not the most beneficial for you. But hopefully you will go not to keep easy for yourself and make it hard only for him, but to make it reasonable for both of you.
Most Helpful Girl
Before you jump into thinking you dont like him in every way. Make sure you just aren't feeling this way because there are underlying issues with you and you are taking it out on him. I know that I tend to do this in relationships and will find things about a guy to not like. So be careful of this.