Hello everyone. I really hope someone can help me clear my head on this topic, because I have been sabotaging my own relationship lately.

History:
I am 24, boyfriend is also 24. I just got out of a 6.5 year relationship and entered into my current relationship shortly after. This may seem quick to some, but the love was gone from my old relationship for quite a long time (being as he was my first boyfriend, I did not recognize that/was scared to end it). My relationship ended very badly, and my unstable ex refuses to talk to me to this day. I wish we could have remained friends and miss friendly contact with him.

Boyfriend had a relationship before ours for 4 years, she cheated on him, they dated a bit more, broke up. She has major anxiety problems and other mental health issues(similar to my ex). Even after the relationship ended, they kept in close contact. He would give her rides to work every day for another year until she moved to a different state (which happened right when he and I got serious). So for them, it’s only been about 4 months of not seeing each other regularly.

The Situation:
My boyfriend and his ex talk probably 5/7 days a week(sometimes more, sometimes less) over facebook messanger. He told me they don’t talk over the phone. This is something that I did not have a problem with at first…I started to get really curious about what they were talking about though. When I asked my boyfriend what they spoke about he’d usually say stuff like “pokemon, memes, video games” etc. These answers were too vague for me.

In my past relationship, my ex told me one day (while under the influence) “I want to have sex with ___, because she’s prettier than you!” This lead to me snooping on his facebook messanger all the time and getting extremely upset at the conversations I’d read between him and this other girl. So my past is kind of interfering with my future here.

So I knew he left his facebook open on his computer so I figured “hey I’ll just read what they talk about and if it’s nothing bad then I have nothing to worry about”. I scrolled through quite a few days worth of convos. Most of it was normal..the stuff he told me they talk about. Then of course I see “I miss you” from him to his ex.
She agrees. He says “I’m happy with my current situation..” “I just wish I could have you both, but I can’t.” “I felt so passionately about you. I don’t know if I’ll be able to feel that way again.”
She says “We just love each other and that’s not hurting anything so whatever”
Then they go back to talking about regular stuff.

I was so heart broken, I still am recalling everything that was said. I couldn’t believe he would say this stuff to another girl. I confronted him when he came home. I owned up to snooping, apologized, and told him I didn’t want to be second best AGAIN to some other person. He reassured me that I wasn’t second best.
He explained that the passionate part was about being naive when they were dating, and that now he has to look at relationships from a critical point of view because she cheated on him. Which I told him, “No..that’s not what you said. What you said to her was about passion and you said you won’t ever feel passion towards anyone else basically”. He stuck to his story of that he didn’t mean he won’t feel passionately about me.
He told me “I don’t want her in the same way I want you. It’s different. Even if I were single today, I wouldn’t be with her.”
The conversation ended with him telling me he doesn’t mind I looked, he would make an effort to always keep me informed of their conversations, etc.

I have done so much googling about this..My feelings are extremely hurt and I have brought up his ex almost every day to him since (it’s been about 5 days), and I can tell it is wearing on his nerves, but he’s trying to be nice. I have been trying to work out with him ways that I can be okay with him talking to his ex, things he can do. I have read websites that say “nope he’s not over her, break up” and websites that say “love is infinite, just because he has feelings for an ex, doesn’t diminish his feelings for you” (the latter being what he’s told me).

So please…I need advice. I’m not really asking if I should break up with him…more so opinions on the situation. Thank you.