Thanks for your question.
In your question, you have highlighted the problem that is probably obvious to this person whom you love. You say you are ready to "accept his teaching for him." This is not a good reason for adopting a set of religious beliefs. Your friend can probably see that your motivation is not a genuinely spiritual one and he is very wise not to encourage you to change just "for him."
What you need to do is to contact a senior member of his congregation [we call it an Ecclesia] and tell him that you wish to have instruction for baptism. If you take instruction on your own and make a decision to dedicate your life to God independently of your relationship with this man, that will impress him very much and convince him that you are serious.
There is nothing wrong in becoming interested in our beliefs because of your attachment to a Christadelphian. However, baptism and membership is a serious commitment and must be something that comes from your heart because you know it is the right thing to do in God's eyes. If you do it only to please this person, your commitment will not last and, down the road, you will have serious problems in your relationship if you and he were to marry.
I hope you have found this helpful.