if i get married can my fiance child support effect me

Short answer: "probably not" if you mean "can the mother attach my wages for my husband's back child support."  At least under NV law -- it is possible that Alabama law is different, and if the obligation is from there, you should ask that question of an AL lawyer.  But there may be no difference in effect, especially if you commingle your earnings in a joint account.  For the time being, maintain separate accounts so your income does not appear in an account with his name on it, which might then be seized.  Long term, the solution is to pay off and eliminate the arrearage.