Denise Richards‘ estranged husband is revealing what ignited their explosive July 4 fight, and subsequent divorce — he claims he caught her cheating, and has text messages to back that up.

In an exclusive interview, Aaron Phypers tells TMZ … he first learned of Denise’s alleged hookup with another man at the beginning of the year, when he found text messages between them on Denise’s laptop.

Phypers claims the texts include several selfies shared between Denise and the other man, and sweet messages like her wishing him “sweet dreams.”

He also alleges other messages indicated they were trying to set up a rendezvous at a hotel, where she would try to sneak him into her room.

He tells us he confronted Denise about the alleged affair, and, ultimately, they decided to stay together — that is, until a huge fight over the July 4th weekend prompted Phypers to file for divorce.

As we reported, Denise has claimed the fight started with Aaron verbally abusing her and demanding his phone.

He says that’s partially true … Phypers says his phone was missing for more than a day, and when he questioned Denise about it, he claims she hit and scratched him — and he later found the phone smashed to pieces in the recycling bin.

He goes on to say he thinks she smashed his phone, because it contained photos of the texts proving she carried on the alleged affair.

Aaron says Denise texted his mom that weekend to say she was going to divorce him — so, he decided to beat her to court and file first.

As you know … he filed for divorce Monday, July 7, citing irreconcilable differences. Denise has yet to respond in court to his petition — which includes a demand for spousal support — but, she did level serious allegations of abuse at Aaron’s hands in a restraining order request.

In the docs, she claimed Phypers owns several unregistered guns, and accused him of slamming her head into a towel rack, leaving her with a gruesome black eye. He has denied laying a hand on her, and told us she sustained the eye injury when she showed up drunk at his office and fell.

A judge granted a domestic violence restraining order against Aaron … who was served with the document while standing shirtless outside his Calabasas home.

Phypers says she got the DVRO in order to make him look like the bad guy — ’cause she knows she’d look a whole lot worse if people found out about the alleged affair.

It appears there were other issues, though, in the marriage. For instance, Aaron shared photos he says were taken inside the house they shared together … and the place is a total mess, littered with a ton of different items. He claims he and his family were also burdened with taking care of her properties and animals.

Phypers has denied all claims of physical and emotional abuse against him … insisting he always treated Denise with the utmost love and respect. He reiterated those denials in the interview.

All that being said, Aaron told us he still loves Denise, and hopes she gets help, because she’s in a bad way these days.