My husband and I we haven’t consummated our marriage yet due to a medical condition on my end (vaginismus). In our marriage contract it states he can’t take a second wife or do muttah without my consent which he knows I won’t give.
Am I wrong to deny him a second wife/muttah if I can’t fulfill this duty due to medical issues?

Did he know you have this problem before the marriage, or did he find out after you two got married? If he knew, then it would not be wrong for you to keep that condition if both of you agreed to it. However if he did not know, that condition is not valid, and he can even end the marriage. If this is a marriage where he cannot have penetrative sex, he does not have to abide by that condition that was made.

I encourage you to seek treatment as best as you can so you can save your marriage and have a more healthy marriage.