Keyshawn Johnson -- Model's Husband Claims Ex-NFLer Had Online Affair with His Wife

Ex-NFL great Keyshawn Johnson is caught in the middle of a model's break-up with her husband -- who thinks she's been cheating with Johnson ... and has filled his court papers with lurid messages.

Alicia Tarry's husband just filed docs seeking an annulment of their 6-month marriage based on fraud. The docs include scores of Twitter direct messages Johnson and Tarry allegedly sent to each other.

The DMs include some racy language about arranging possible hook-ups between Alicia and Johnson. One DM says, "Send me a p**** shot." The response, "I'll get one in a few sorry have a guest over."

It appears Tarry's husband got hold of her phone or her Twitter account ... because one of the alleged DMs to Keyshawn -- says, "Please leave my wife Alicia alone."

Alicia tells us she did not cheat with Keyshawn, and further ... she says the DMs "appear suspicious" and were illegally obtained.