"I struggle to cope with this erratic behaviour and I'm a grown woman, how the fuck is a teenage boy supposed to deal with it"

Well exactly. Short answer is that neither he or his sister can - or should be expected to. But you're still there and your children have no say in the matter.

Why are you still there, what is in this for you?. What is there to love about him exactly?. What do you want for you and your children?.

On a wider level what are you both teaching them about relationships here?. All that is happening here is a load of dysfunction and damaging stuff which is being taught to them by both of you.

BTW how is he with other people, does he behave in a similar manner towards them?.

His behaviour is emotionally abusive - there is no way that you should be having joint counselling.

his therapist says he lives in the past and needs to concentrate more on the here and now

some days I wish I'd never met him

but other days I love him so much

I don't knwo what I expect anyone to say I just need to get it out

we only established the depth of his resentment/jealousy towards me since he started therapy, he resents my job, the fact that I earn more than him, that I work full time and we have to share the housework/care of the children but yet we always have so I don't see how this is suddenly become more of an issue.

am a regular and have namechanged

Dh and I have ben having problems for some time now, he is having therapy, I've joined him for a couple of therapy sessions, it's been a lifeline tbh - but I don't know if it's enough.

This is 17 years worth of relationship struggles, so far too much to explain in one post.

We have 2 dc but a lot of his therapy revolves around him and his behaviour towards our teenage son, dh has lots of resentment and issues and basically takes it out on ds and me (verbally never physically).

He has quite serious health problems and suffers from depression he is and always has been a cup half empty type of person, whereas I'm a cup half full.

I feel like I'm living with a Jekyl and Hyde type character - he can be horrible/moody/snappy but this can flip very quickly and he can be lovely.

for example - ds wanted a game for his xbox, its £40, dh (being lovely dh) offered to buy it if ds paid half. He said he would pre order it so ds got it on the 23rd (doesn't come out till 26th). Ds was obviously really pleased and did babysitting and odd jobs to earn the £20.
I was quite surprised dh had offered to buy this game for ds as it wasn't xmas or birthday and for us it's quite unusual to do that, but I thought it was a nice gesture and ds was really happy.
Dh then decided he didn't have the money to buy the £40 game and told ds he was cancelling the pre-order .
Ds obv very dissapointed but didn't make a fuss about it.
Dh told me after he'd cancelled it, I told him its ok I'll pay for it.
Dh gets stroppy saying I shouldn't have agreed to let ds babysit in lieu of the £20 (iyswim) and dh actually wanted the £20 in his bank account (it all gets very petty).
Dh then re-orders the game, but doesn't tell ds.
Then dh tells ds he'll have to wait till dh gets paid to get the game, when I've already told dh I'll pay and I know he has pre-ordered it (they are both by this point having a row about it that dh started).
So I send ds and dd out of the room and stop dh and tell him what he is doing.

it goes on and on

the whole buying of the game thing is a crap example but is just that, an example the lovely dh wanted to do somthing lovely for ds, then the horrible dh wants to take it away WHY?.

he gives - he takes away - he gives - he takes away

he does this emotionally as well, constantly, I struggle to cope with this erratic behaviour and I'm a grown woman, how the fuck is a teenage boy supposed to deal with it

We've come very close to separating recently, but on one hand he says, if you don't like it you know what you can do (leave) - then tells me he won't leave as it's his house (I pay half the mortgage)- then tells me he won't let me take the dc - then tells me he knows he makes me unhappy and I would be better off without him but he does love me - then apologises and becomes lovely dh again.

my head is fucked

I really am not in a position to go anywhere, I feel backed into a corner and just when it seems too much to bear - lovely dh reappears.