mine get firm but never produced an orgasm or cum. At school one guy could cum by rubbing his nipples . he let me do it sometimes
Never try orgasm/cum : simply enjoy whatever your body gives.
If no you are creating expectations on your mind which makes things harder.
Relax, put on a confortable position, don't think about anything simply enjoy whatever your body gives and slowly massage your chest avoiding them.you can make circles from the external part until you arrive the aureolas, enjoy the change of Textures, how the hot pass between your chest to your fingers..
Without touching the nipples go on making circles from the aureolas to the external part.
You can change to others way to massage.
Other which works great is the "bread dough" (I call this way as you have to imagine your hands are working the bread dough : compressing, pressing down,..
The more you tease them the best.
Randomly after some time press slowly the tip of one nipple.
Enjoy the feeling but back to the massage.
As I said don't worry about no orgasming, simply enjoy the feelings.
Tell us how you felt.
Enjoy it!