It may appear that  your spouse's SSDI is being added to your income, but you still wlll usually come out better filing MFJ.
The statement "his disability is not enough to file" may be changed by the marriage. If you file as MFS, your spouse's status also become MFS and his SS disability income taxable

Social security (including SSDI) becomes taxable when your income, including 1/2 your social security, reaches:
Married Filing Jointly(MFJ): $32,000
Single or head of household: $25,000
Married Filing Separately and lived with your spouse at any time during the tax year: $0