Your Immigration Expert
Securing Your UK Visa From Cape Verde
The best approach is for your partner to apply for a visitor visa. Be aware that he will need strong links to Cape Verde or they may refuse him on intentions to return as he has a UK partner. Not that he could switch visas while in the UK to a more permanent option.
The UK Visa Office will also require evidence of funds to show he can afford his trip. He will need to contact the British Consulate in Dakar. I hope this is a good starting point.