Hi Gemma and a warm welcome to the forum
Firstly with regard to your partner's ongoing training, it may be possible to include an allowance for these costs, and I have certainly done this on many occasions for clients of my own.
With regard to the joint debt, if he enters into an IVA, you will be chased for the full repayment - so would you be able to afford to pay these ongoing payments from your salary alone?
Your own credit rating is unlikely to be affected by his IVA, but it would perhaps be better to curb the spending on credit and try and live within a budget for a while. Your partner will need a lot of support from you during his IVA, and it already seems that he is getting a lot of that!
Please continue to post any queries you have relating to the process, so that others can also share from the discussions.
Regards, Melanie Giles, Insolvency Practitioner