BF texted his ex that he missed her 2 years into our current relationship

I really love my bf and have never been given a reason to not trust him. But one day I had this awful gut feeling something was going on or was wrong so I checked his phone (I know this was bad.
I know) and I saw that he had deleted a message he had sent to his ex girlfriend saying he was thinking about the past and that he hoped everything was well and he missed her. I immediately woke him up and asked what the **** this was about and he came clean and said that for awhile he’s been depressed and abusing drugs and alcohol and had been making bad and reckless decisions for weeks (he had gotten into a fight with one of his friends a week prior). I asked if he actually wants to be with her and he was adamant that he didn’t want anything to do with her, he just sent the message in a high drunken haze and then deleted it immediately because “I knew how stupid it was to do that right after I had sent it”. So, I told him if we’re going to stay together he needs to delete her contact (he did immediately) and go sober and go to AA meetings, and therapy and he’s been doing all of those things. Do you guys believe his story? Do you think he wants to be with me or should I break up with him? He’s been putting in the work to make things better for awhile now but I can’t help but still think about it.

I really love my bf and have never been given a reason to not trust him. But one day I had this awful gut feeling something was going on or was wrong so I checked his phone (I know this was bad.
I know) and I saw that he had deleted a message he had sent to his ex girlfriend saying he was thinking about the past and that he hoped everything was well and he missed her. I immediately woke him up and asked what the **** this was about and he came clean and said that for awhile he’s been depressed and abusing drugs and alcohol and had been making bad and reckless decisions for weeks (he had gotten into a fight with one of his friends a week prior). I asked if he actually wants to be with her and he was adamant that he didn’t want anything to do with her, he just sent the message in a high drunken haze and then deleted it immediately because “I knew how stupid it was to do that right after I had sent it”. So, I told him if we’re going to stay together he needs to delete her contact (he did immediately) and go sober and go to AA meetings, and therapy and he’s been doing all of those things. Do you guys believe his story? Do you think he wants to be with me or should I break up with him? He’s been putting in the work to make things better for awhile now but I can’t help but still think about it.