Truth isn't always easy, but honesty needs to be present at all times if you are to form a union. Be wise, be gentle, not accusing. His family will always be present... don't cause enemies. Possibly say "I think you always put others first, which is one reason I love you. I'm here to put you first & take care of you, & I think your family is used to you putting yourself last. For us to have a healthy relationship of our own, I think you should say no sometimes...." for ex. That way he sees it's because you care. Just be careful what you say & how. Use nice soft tones... you do need to be able to communicate.
Honesty is the best policy. Don't keep anything from him and just tell him, nicely. Say "I love you very much. I don't like to see you in pain or being manipulated. I think that your family has been manipulating you a bit. You are so sweet and kind, and I understand you. I feel that you should be a little less soft around your family. I wanted to tell you the truth. It's hard, and if you're mad, I understand," for instance. Don't use words like "push-over" or "using" because that may offend him. Best of luck!