OK, some suggestions, just to get your own ideas rolling:
I don't feel like he enjoys being with me except in bed,
Tell him that, in those words
doesn't get involved with DCs,
Tell him how this makes you feel. See if he comes up with spontaneous suggestions, or whether he goes into blame-shifting mode.
he was working away a lot last year, so felt a bit like a stranger when he was home.
Ask yourself why this is still bothering you now, when presumably (as I read it) the working away has stopped? What unresolved issues from that time still need to be resolved?
He spends money we don't have on 'toys' for himself,
Tell him how this makes you feel. See if he comes up with spontaneous suggestions, or whether he goes into blame-shifting mode.
Buy toys for yourself too...
but makes me feel bad for spending on DCs/food/clothes etc.,
Stop feeling bad: these are necessary and useful household purchases.
Don't defend them.
I feel like I'm on my own a lot, as even when he's here we have little in common.
Tell him how this makes you feel. See if he comes up with spontaneous suggestions, or whether he goes into blame-shifting mode.
I thought it would be good to share a hobby and that we could both run and take DCs out on bikes at the weekends, but he prefers to go alone and started getting competitive about how far he'd run etc.
Ask yourself why this makes you feel so rejected. What are the underlying, unresolved issues?
Ignore any competitive statements, since you don't want to enter into a battle about who's better between the two of you.
Tell him how you feel.
Suggest joint running.
Above all: KNOW YOURSELF: your needs, your wants, your feelings. You have a right to all of these. And only you can put forward your needs, your wants, your feelings. You can't expect anyone to fulfill these for you, but you can decide how to act if these needs/wants/feelings of yours are not being met.