The more I read of your descriptions of him the more I feel like I am playing abusive man bingo, unfortunately.
They start out nice, that's how they lure you in as if they started out as bad as they can be you wouldn't entertain them as a possibility. They also often do have some positive traits, but even the worst people do.
I don't think most abusers plan to consciously be abusive at the outset, but the underlying motivation is to hook in someone to meet all their needs or wants without that person being able to demand much of anything from them, and whose boundaries they don't have to respect. Thinking of it that way, do you feel you see signs of this even in his 'nice,' behaviour?
He's not respecting you or your boundaries, and trying to get close to you quickly and overwhelm you (either with 'positive' attention or sulking etc). I wonder if he reacts badly to you rejecting some 'nice' or supposedly positive actions you find too much or that aren't your thing? Telling you how you should feel, maybe?
With the depression and breakdowns statement, this worries me a lot in the context of other issues. I see it as potentially preparing you to feel sorry for him and as an excuse for his behaviour. Something to pull out later to manipulate you with, and to keep your attention on him and his feelings instead or yours or your son's.
I see something like this coming:
'Don't ask me not to criticise you, that's so mean and I am depressed. You are destroying my mental health.' -- When it's the other way around. He's the mean one and harming you, but making it about himself and turning your justified grievances around.
Or if he feels you are focusing too much on someone else or yourself I can see him having a supposed panic attack or break down. Then he gets all the attention and care and can pretend to be heroically struggling.
And:
'You can't leave me I am devastated and have depression,' and then mummy dearest texting about the devastating impact on him your ending the relationship has had...oh, wait...no, we've already had some of that.
Then you are made to feel awful, to doubt yourself and take him back out of pity. If that's happening you are being drawn into the cycle. I'm waiting for talk of suicide if you leave/supposedly hurt his feelings or pull away.
It's weird to be so open about depression and mental break downs with a new partner. It can put people off so they take time to build up trust and are more likely to down play such things. My husband has had challenges with depression but he took time tell me and when he did he emphasised how he took responsibility for his own mental health, for getting treatment and sticking with it. He didn't try to make me feel he was vulnerable or might need me to treat him with special care or sympathy. He wanted me to know while it had impacted him he had strategies to help himself should it re-occur, he hasn't even acted like it's my responsibility to fix him or manage his moods or might need special handling by me.
When it comes up like that it's a red flag.
But there are a forest of them now. He needs to go before it gets worse.
If you find you are repeatedly going for men like this it's probably linked in some way to your upbringing and self esteem. Women's Aid might be able to help with counselling so you can spot these men more easily...and it is also easier to see when it's not you it's happening to, like a lot of things. So, try not to feel bad about yourself for not seeing this guy coming or you won't find someone lovely eventually. You just need a bit of help.