My husband and I had a threesome but he won't let it stop there

We are young and newly wedded so I never imagined this to be an issue, but it seemed as if my husband was becoming bored with our sex life. I'm always trying to spice it up with sexy outfits, New positions. I've tried being more romantic and I've tried just letting him be rough and do whatever he wants with me, but nothing seemed to make him more into having sex with ME. So I decided to take it an extra mile and we got drunk one night and I allowed an other girl in. It was a one time thing and not too long ago, but now our sex life is getting worse. He told me the other day he met this girl on tinder. Then he started snap chatting her and the messages erase so I have no clue what they're saying. He came home last night from work and I tried to have sex with him and he said he was tired and didn't feel up to it. Then 5 minutes later he asks if anyone has gotten ahold of me for a threesome again. He tells me today that the girl he met on tinder and had been snap chatting gave him her number and they'd been texting. When I looked at his phone the messages were all gone and he said he accidentally deleted them. I also found on his phone that last night when he went to shower, instead of just having sex with me, he watched porn.. I thought it was weird that he locked the door when he went in the bathroom.. I mean, hello, we are married! It all started with a little one night fun and he's taking it too far. Even if he is telling me about this other girl he met on tinder he is still going to lengths to make sure what they are talking about is never seen by me. Someone please help me understand!