Search Results: admitting mistakes

My boyfriend & I've been together for a little over 3 years & throughout these years we've had our share of rough patches & messy fights. He's lied to me several times & sometimes the lies were so insignificant & unnecessary it baffles me on why he even lied (e. g. I asked him to walk the dog. when I got home I asked if he had & he looks me in the eyes says yes, I even asked him "are you sure you?" & he stuck to his lie even though I knew he was lying because there was no collar on the dog & when I confronted him he finally admitted he lied).
A month ago we had an extremely ugly fight to the point that he packed some of his clothes & stayed at a friend's (we live together). After 2 days with the help of a friend who mediated we talked without fighting & agreed we have so much at stake & it is worth trying to work things out, maybe try couples counseling. Things started to get a bit better & a 2 weeks after on our anniversary he gave me a promise ring. That made us both try to work things out no matter what & he made a promise to me that he won't lie anymore, 100% honesty without white lies our half-truths.
Still, the skeletons in his closet keep popping out & he lied again. I've never lied or been disloyal even though he slept with a girl last year when we were on a break & downloaded 3 dating apps the two nights he stayed at his friend's after our fight. I've taken him back after everything he has done & put me through & hurt me because I just don't want it to end. Im so emotionally deep in this that I can't tell anymore whether its love or I've gotten used to him or its convenient having him be there always or if its that I rather stick through in hopes of making it work, out of dreading to go back to being on my own and having to start dating all over again from square one.
Also ending it would be so messy & painfully heartbreaking as we have so much history, mutual friends, lease contract, a dog, etc.

Have I made a mistake for staying? Why can't I want to leave still?