Partner in bridal party of another wedding

Your partner is making a compromise to be in his friends wedding party as he would be the groom to you for your wedding. He does share his time equally and get things done for his friend as for your wedding, I say he's on the right path. The balance is more towards his friends wedding and not yours, then there's something to deal with and make it the right balance for his duties to accomplish. Life is such that obstacles come so close in time and he does know what is important to you as him to make everything work. A checklist is a good way to know for both weddings is being completed and you feel rest assured he is on the same page with you.

I don’t think it’s a problem at all. People often get married at similar times to their friends so this isn’t a unique situation. If your partner starts neglecting his own wedding duties, sure sit him down and let him know you’re worried he’s prioritizing this other wedding rather than his own. But if he’s just participating in this other one like a normal wedding he’s just supporting his friend and planning/attending a few events for this person. Shouldn’t be an unreasonable time commitment.

Either he agreed to be in the bridal party before your engagement or he did so knowing full well what responsibilities and obligations are for your wedding and felt he can handle both. Regardless of which, unless he has demonstrated that he is neglecting his own wedding or is actively pushing his own wedding plans for the sake of his friend's, I think it's unfair to make assumptions that he is prioritizing another's wedding over his own.