As we previously reported, the former TCU superstar has been in SERIOUS trouble with the law after he allegedly broke his girlfriend's jaw in an altercation in March 2018.

Boykin was out on bond while he was fighting the case in court ... but he was thrown back in jail in November after cops say he failed to charge his electronic monitoring device.

But, while the 2015 2nd Team All-American has been in custody ... investigators have been working on other cases involving the 26-year-old, which have now resulted in MORE criminal charges.

Here's a brief summary of what Boykin is now accused of:

Back in January 2019 ... cops say Boykin ran a memorabilia scam, where he took Venmo payments from two people with the promise of giving them TCU items in return.

Problem is ... cops say he never delivered on the goods -- and just hit him with two theft charges this week.

Officials also nailed the guy with an additional theft of service charge earlier this month ... stemming from an alleged incident at an Arlington, Texas-area hotel back in October 2019.

Cops say Boykin checked into the place on Oct. 29, but after his reservation was canceled because of fraudulent credit card use ... he left without properly paying the bill on Oct. 30.

Boykin had HUGE NFL potential during his early college days -- at one point, he was considered a top QB draft talent (with 1st or 2nd round buzz). But, things went south for the QB in a hurry, especially after he was charged with assault for fighting a police officer after he was thrown out of a bar days before TCU's 2015 Alamo Bowl game.

Despite all his issues ... Boykin still got a shot with the Seattle Seahawks from 2016-2017, but he pissed it all away with multiple arrests in 2017.

Now, his NFL career is all but over ... and he's facing DECADES in prison with all of the allegations against him.