I think he would've dumped you again (after getting back in contact) ... even if one of his partners (presuming there was more than one) hadn't fallen pregnant.
He planned to leave, ended your ltr with a text and left. He was clearly out enjoying his freedom, hooking up, probably doing do without condoms.
You think.him getting back in touch was a sign he was going to get back into a relationship with you (and it was going to beall secure and perfect) but the fact that he ended you'd relationship, quite brutally at that, moved on quickly etc. makes me think you're deluding yourself.
Occasionally people do get back together after a break up, but the way he ended it, the way he behaved .... I think he was more likely to be one of the ones with whom him ending it means the relationship was going to end sooner or later; he was just going to mess you about for as long as you let him or until he met someone he got involved with.
So, as unpleasant as it is to hear, whether his relationship works out with this woman he knocked up or not .... Doesn't actually matter at all. I don't think it was her or you .. I think you'd have been dumped again (or never gotten back together again properly/officially).
Are you depressed; you seem to be so excessively negative about your own prospects of a relationship with someone else ... And so excessively idealising of him and of his new relationship.
You seem to have convinced yourself that he was your only chance ... You're only 34/35. He isn't.
The longer you spend focusing in him, wailing, wallowing in this .. the longer you're wasting to make new connections, meet new people, expand and change your social life, the circles you move in (not super easy under current circumstances but ..), one of which could lead to meeting a partner.
Turn it around; what would your impression be about a guy who was going on like this about his ex gf who's gotten knocked up by one if her partners after him?
Would it be an attractive impression?
A stable Impression?
It's great that you're having counselling, do you think it's really helping?