Is it his visit to Portugal this week that convinced you ?
Yes and no. His interest in the idea of a coalition was good. But from what I've seen and heard in the meanwhile, Hamon is in love with his idea of the EU, which is not really much differnet from the current one, and is one that: 1) I do not believe can work; 1) even if it did, I can't approve of. I'm afraid he'd do anything to shore it up were he president. And when it inevitably failed (for economic and political reasons I don't want to get into here, again), then Le Pen will have the Élysée - and a majority in the National Assembly!
The current socialist PM here in Portugal is pragmatic enough that he'd be out of the EU in an instant
if he saw it crumbling. He's not in love with it, just believes that there is currently no alternative (a bad position imho, but at least he won't chain the country to a corpse). There are three reasons the current "coalition" here keeps together. Two are noticed by everyone: the right-wing opposition is led by people who are profoundly despised (from the former government), tourism has kept the economy afloat albeit with low-paying jobs (it'll crumble as soon as interest rates rise by even a couple percent, and the portuguese government no longer controls interest rates, the ECB does). The third is that all the politicians who believe the current situation unsustainable (the EU and its policies) are willing to do some quiet preparations now and wait for conditions to change abroad before breaking with the EU rather than go it alone. But even if France or Italy or the ECB (Germany...) don't bring it down this year, brexit will create an alternative in the next - then they'll demand action and this coalition will be put to the test.
Long story short: Hamon does not seem pragmatic enough about the EU to me. He holds it as some kind of "core value". Now Melenchon has publicly challenged him: the EU or France? Hamon can reply that the EU
must change radically, or France will be out. But he won't: he's in love with the idea of EU so much that he'll rather lose he election that create a coalition.
If Hamon were like the socialist leader here, he'd always equivocate and avoid profess any loyalty to the EU. Publicly show that he wasn't
personally committed to the idea of the EU. But it's too late for that I'm afraid.