"He is an utterly devoted and amazing dad & family man" posters always say this when pps criticise the guy who is clearly behaving badly!
NO he's NOT!
If he WERE you would not be feeling sad, lonely, desperate for adult company, let down by his actions.
YOU are his family too, plus men who really care for their families understand that supporting the mother is a key part of supporting their family.
"It’s just emotionally i feel unsupported by him." What is 'just' about that? That's a really important thing to do especially for a heavily pregnant, struggling partner who is in pain!
"But I have been trying to see his side of things aswell as this and playing football once a week is the only things he does for himself" Again NO it isn't - his going to the gym AND for a run every night/most nights is ALSO him having time to himself - when do YOU get find to yourself? Do you even get a bath in peace with him available to see to kids?
"no they were not planned I seem to be very fertile as we had took steps to avoid pregnancy." What contraception were you using?
I think you need to consider the possibility he's feeling resentful of having 3 children in such a short space of time. It's not right as he's half responsible but if you're to have a chance of this relationship surviving he needs to be honest with you.
Also it very much sounds like it is you he's avoiding which is what also makes me think both "resentment" and "possible ow".
A less likely possibility but still a possibility is that he is genuinely an exercise addict. It's not a common addiction but it can happen and if it is the case then he needs help to address it as any addiction is unhealthy.
But other reasons are more likely.
Is he exercising every night? How long is he out for?