DO NOT TELL HIM HE HAS A SMALL DICK.
Lemme start this comment with a small (pun not intended,) foreword:
We live in a society wrought with fragile masculinity, and if you don’t care if you hurt someone’s fragile feelings, skip my comment.
Men in general have an ego tied to their dick size. Hell, there’s an entire chapter dedicated to it in human sexuality courses in college. If you want a healthy sex life, the last thing you should do is break down someone in that department. He could develop a sexual anxiety issue that will never go away.
With that being said, YOU DESERVE TO HAVE AN ORGASM. If you care about this person and he cares about you, you’ll work together to make that happen. You could say things like “it takes a lot to get me off.” Or “I’m like the vast majority of girls that needs clitoral stimulation to get off.”
Let me rephrase my first thought about fragile masculinity: men are absolute idiots. If you want to pump them up all you have to do is make a big deal out of little things (pun not intended.) If the give you 3 inches (pun not intended,) you could act like it’s a mile. If he gets you off orally or with toys you could act like it was the best thing that ever happened. My girlfriend says “I give her the best orgasms.” Which I know is bullshit, but it makes me feel good in the moment.
Another thing: I don’t know you or him, but if he’s asking if you feel satisfied or if there’s anything he can do, chances are he knows there’s an issue. Take those moments to guide him in the right direction to where you both are satisfied.
TLDR: you may hurt his feelings by outwardly saying he isn’t the right size. Use the opportunities where he asks to maybe have a healthy sexual relationship.