Bad credit shouldn't be the reason stopping you from tying the knot. If you have bad credit and your fiance has excellent credit, you'll each have that same credit after you get married. Marriage doesn't combine credit scores, either for good or for bad. The only way your bad credit could hurt your spouse is if you co-sign a loan together that doesn't get paid.
The difference in credit scores could make it harder to take out joint debt, like a mortgage or auto loan. Your bad credit might cause the lender to decline you, making your spouse be the sole applicant or requiring a co-signer.