Can't quite get over the cocklodger/money grabbing comments. Are you all for real?!?
OP has been raising their child as a single parent for 2 years, while the mobile sperm-donor flits around the country focussing on nothing but furthering his career, while contributing just 20% of his earnings to raise his own child.
Then has the audacity to set up a permanent base 4 hours away from where his child is already well established, then call in 'I think we should have a stab at living together'!
No, it's not in any way unreasonable that he continue to make financial contributions to the arrangements OP!!! Potentially you could dress it up differently - you plan to rent your place out, take the net earnings from that for 3-6 months as savings/security/relocation buffer to cover you in the event that it all goes tits up & you have to move back there again. Then all other household costs in the shared place get split pro-rata to your take-home salaries (after student loan repayments). Your rent goes back in the household pot once your moving buffer is built up - of if he owns the new place, you keep your rent as he's building his own equity.
Agree with most that you should line up a job to move to though. Very sketchy without.
Also, these arrangements are almost the least important thing you haven't spoken about! What about wills, custody of DD in event of death of either of you, life insurance/pension names parties for each other, who will cook, clean & taxi in a shared house. Is he working research 9-5, or hospital shifts including weekends? Who will take leave when DD is sick in new arrangement & you're removed from current network, building Bradford Factor in a new job, and you're in a town DP has arbitrarily chosen for the next X months convenient to his career development? When will the next move be? Where to?
It definitely feels like the onus on the 8 hour round trip should be on him for a while yet, until:
A your relationship is grown up enough to have ALL the above conversations, plus whether a civil partnership would be a more secure & appropriate arrangement under which you could make such a move
B he's had enough 8 hour round trips to spend time with the child he created to properly contemplate why in the name of dog he didn't look for a permanent role closer to where they lived in the first place if either of you are actually important to him?