Do woman give blowjobs less often the longer they are with someone?

My girlfriend has basically stopped giving me blowjobs after we have been together over a year. The first 6 months I would get maybe 1-2 a month, now it's zero. I don't think I've gotten one in 3-4 months. I was just wondering is this is a trend amongst women?
Do woman give blowjobs less often the longer they are with someone?
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