His mother might be "a nightmare" but that does not absolve him of responsibility. He is behaving like a little boy rather than an adult. He wants to get back together with you - but has he changed?

Like you write, he is too enmeshed with his mother. IF you give him another go and he hasn't changed, be prepared for a repeat performance. There will be THREE people in the relationship (i.e. a little boy, his mother... and you), and you will be the one left out. Is that the cost you are willing to pay in the name of 'love'?

What do you mean ''offering him therapy"?! First off, he should get (and pay) for his own therapy himself, as a grown man. Secondly, until he realises how he is allowing 3 people in the relationship, therapy will be a waste of time and money.