My ex wants to stay friends instead of being in a open relationship he thinks it’s a better chance getting back together... is that true?

Answer 1

Do not even ENTERTAIN getting back with an ex.
The two of you broke up for a reason, and the reason is still there. It will produce the same result.

It takes 10-30 years, or even "never" to get over our inner "reasons". Don't expect change to be permanent or even possible in under 10 years.
Not enough to keep you two from breaking up again.

BEST thing to do is to cut off ALL forms of contact for AT LEAST a year.
Then a year from now re-evaluate: if either of you is not TOTALLY over each other, continue with the non-contact. And whoever is not totally over, needs to get some therapy.