@ ubuntu, a fetish is usually classified as someone becoming sexually aroused by objects not related to sex or intimacy. Underwear, particularly things and lacy underwear are designed to be eye-catching and aesthetically pleasing. Your arousal to this is absolutely normal. My partner has a very similar thing for lacy underwear. A girl can go from a 5 to a 10 on the "would do" scale just cos of the underwear. It's fine, I don't object at all because it's something I can be involved with as his partner.
I think if you feel so strongly that it's upsetting you then maybe a therapist would be a good place to set things straight in your head.
All the best.I really hope you find some way to be ok with this and happy in yourself.