It's really disgusting that he had sex with you the night before. My god what a MASSIVE arsehole🤬
This guy is very likely an emotionally chaotic, immature, deeply cowardly, narcissistic, selfish avoidant who can perform affection for a while but eventually reverts to type. He and his ex have had a volatile relationship, probably because he's an avoidant and she's trauma bonded to him. When you and he started talking about getting a house and he invited you to meet his family, the commitment freaked him out and he decided to ditch you and get back with his ex.
To be able to ditch you, he likely spent the preceding days or weeks building an internal case, where he dehumanised you and dissociated himself from his conscience. This is shown by the fact that his breakup text felt impersonal and he said "you wanted me to [breakup] by text" (which was bullshit). The latter is particularly revealing: he created from thin air an excuse for the horrific way he conducted the break up. He literally pretended to himself - because it assuaged his conscience - that YOU would prefer to be broken up this way. It shows what a screwy fuckwit this guy is.
He probably deleted the hearts and kisses text because seeing it again created cognitive dissonance in him.
I know you're hurting badly and feel like you can't trust yourself. But it's not your fault, because this guy is a lying screwball, and women aren't trained to detect these freaks.
If you look back, you will probably see clues that this guy wasn't safe:
A. "a few months into our relationship, he told me 'So .. I’ve had a couple of challenges with my ex - I’ll not bother you with all the details but it’s all resolved and she is clear that we are friends/co parents only"
"SHE is clear that we are friends/co parents only" = he wanted more.
B. "and I am all yours my darling. I truly value how honest and genuine you are my lovely and I am completely yours and just want you my love." Ardent avowals of love a few months in is often a sign of a lovebomber.
C. His story dissing his ex: her lying on the sofa ignoring him, them repeatedly breaking up and getting back together, her fleecing him. Knowing what you know now, do you think that was true? I rather feel sorry for her that this messed up fucker is back in her life.
You might find Burnt Haystack helpful: it shows how you can use rhetorical patterns to identify freaks like this creep. There's a lot of women there who have been burnt by men like this.
Please don't internalise this. How he behaved was ALL about him, not you.