Hmm...I like to think that version of Matteo is gone and buried ....The Matteo we see at the end is a man who has matured...and finally understood that holding love hostage is a futile undertaking..It never ends well. I believe when Noah saved Eros, it sort of broke through all the madness and and made him realise that Jace was never really his after he got with Noah.
You are the author and this baby is yours..whatever you choose will definitely be the right path..I like to hazard a guess that if there is a book 2, there will be another threat ..Someone who is even more unhinged that will be a problem for Noah,Jace or both if Providence wins and they do get back together..and that Matteo might be an ally. That's just me though😂