Hello I am new here. I understand what you are going through. I had the same problem with my husband.
One thing you could try is to masterbate together. Start there then as you both get used to it start helping him. Have him show you how hard or soft he holds it. Sqeezing to hard or to lightly will change things. After he has cum to your hand ( with out his) it will be easier for you to add in your mouth. Start at the top and work your way down slowly. Soon you will have cumming everytime.
Just remember this may have worked for my husband, it may not work for your boyfriend.
